Limit related problems in differentiation

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Suppose $alpha$ and $beta$ are two roots of the equation $ax^2+bx+c=0$. Find
$$lim_xtoalphafrac1-cos(ax^2+bx+c)(x-alpha)^2$$



Please help me to solve this calculus problem










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up vote
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Suppose $alpha$ and $beta$ are two roots of the equation $ax^2+bx+c=0$. Find
$$lim_xtoalphafrac1-cos(ax^2+bx+c)(x-alpha)^2$$



Please help me to solve this calculus problem










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  • 1




    Welcome to Math SE! Your image is barely readable. Since the question is so short, how about type it in MathJax?
    – Toby Mak
    1 hour ago






  • 1




    Welcome to MSE. It will be more likely that you will get an answer if you show us that you made an effort. This should be added to the question rather than in the comments.
    – José Carlos Santos
    1 hour ago










  • What kind of rules can you use?
    – Dr. Sonnhard Graubner
    1 hour ago






  • 1




    Instead of suggesting an edit from a different account, please use your original account and click on "edit" to add details to your question. As it stands, it is not possible if the suggested edit is by you or by someone else pretending to be you. On a side note, using your original account, you can add comments to your own posts irrespective of reputation.
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up vote
1
down vote

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up vote
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down vote

favorite











Suppose $alpha$ and $beta$ are two roots of the equation $ax^2+bx+c=0$. Find
$$lim_xtoalphafrac1-cos(ax^2+bx+c)(x-alpha)^2$$



Please help me to solve this calculus problem










share|cite|improve this question









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Ramisa Samira is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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Suppose $alpha$ and $beta$ are two roots of the equation $ax^2+bx+c=0$. Find
$$lim_xtoalphafrac1-cos(ax^2+bx+c)(x-alpha)^2$$



Please help me to solve this calculus problem







calculus






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edited 1 hour ago









GoodDeeds

10.2k21335




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  • 1




    Welcome to Math SE! Your image is barely readable. Since the question is so short, how about type it in MathJax?
    – Toby Mak
    1 hour ago






  • 1




    Welcome to MSE. It will be more likely that you will get an answer if you show us that you made an effort. This should be added to the question rather than in the comments.
    – José Carlos Santos
    1 hour ago










  • What kind of rules can you use?
    – Dr. Sonnhard Graubner
    1 hour ago






  • 1




    Instead of suggesting an edit from a different account, please use your original account and click on "edit" to add details to your question. As it stands, it is not possible if the suggested edit is by you or by someone else pretending to be you. On a side note, using your original account, you can add comments to your own posts irrespective of reputation.
    – GoodDeeds
    1 hour ago













  • 1




    Welcome to Math SE! Your image is barely readable. Since the question is so short, how about type it in MathJax?
    – Toby Mak
    1 hour ago






  • 1




    Welcome to MSE. It will be more likely that you will get an answer if you show us that you made an effort. This should be added to the question rather than in the comments.
    – José Carlos Santos
    1 hour ago










  • What kind of rules can you use?
    – Dr. Sonnhard Graubner
    1 hour ago






  • 1




    Instead of suggesting an edit from a different account, please use your original account and click on "edit" to add details to your question. As it stands, it is not possible if the suggested edit is by you or by someone else pretending to be you. On a side note, using your original account, you can add comments to your own posts irrespective of reputation.
    – GoodDeeds
    1 hour ago








1




1




Welcome to Math SE! Your image is barely readable. Since the question is so short, how about type it in MathJax?
– Toby Mak
1 hour ago




Welcome to Math SE! Your image is barely readable. Since the question is so short, how about type it in MathJax?
– Toby Mak
1 hour ago




1




1




Welcome to MSE. It will be more likely that you will get an answer if you show us that you made an effort. This should be added to the question rather than in the comments.
– José Carlos Santos
1 hour ago




Welcome to MSE. It will be more likely that you will get an answer if you show us that you made an effort. This should be added to the question rather than in the comments.
– José Carlos Santos
1 hour ago












What kind of rules can you use?
– Dr. Sonnhard Graubner
1 hour ago




What kind of rules can you use?
– Dr. Sonnhard Graubner
1 hour ago




1




1




Instead of suggesting an edit from a different account, please use your original account and click on "edit" to add details to your question. As it stands, it is not possible if the suggested edit is by you or by someone else pretending to be you. On a side note, using your original account, you can add comments to your own posts irrespective of reputation.
– GoodDeeds
1 hour ago





Instead of suggesting an edit from a different account, please use your original account and click on "edit" to add details to your question. As it stands, it is not possible if the suggested edit is by you or by someone else pretending to be you. On a side note, using your original account, you can add comments to your own posts irrespective of reputation.
– GoodDeeds
1 hour ago











3 Answers
3






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up vote
2
down vote













HINT



We have



$$frac1-cos(ax^2+bx+c)(x-alpha)^2=frac1-cos[a(x-alpha)(x-beta)]a^2(x-alpha)^2(x-beta)^2a^2(x-beta)^2$$



then refer to standard limit as $tto 0$



$$frac1-cos tt^2to frac12$$






share|cite|improve this answer



























    up vote
    2
    down vote













    Recall that $lim_t to 0 frac1-cos tt^2 = frac12$.



    We have



    $$frac1-cos(ax^2+bx+c)(x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)](x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)][a(x-alpha)(x-beta)]^2cdot a^2(x-beta)^2 xrightarrowxtoalpha frac12a^2(alpha-beta)^2$$






    share|cite|improve this answer
















    • 1




      @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
      – mechanodroid
      1 hour ago

















    up vote
    1
    down vote













    Hint. Use the Taylor series of
    $$
    cos(a(x-alpha)(x+beta))
    $$
    around $alpha$. That is
    $$
    cos(a(x-alpha)(x+beta))= 1-frac12(alpha-beta)^2(x-alpha)^2a^2+o((x-alpha)^3)
    $$






    share|cite|improve this answer






















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      3 Answers
      3






      active

      oldest

      votes








      3 Answers
      3






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes








      up vote
      2
      down vote













      HINT



      We have



      $$frac1-cos(ax^2+bx+c)(x-alpha)^2=frac1-cos[a(x-alpha)(x-beta)]a^2(x-alpha)^2(x-beta)^2a^2(x-beta)^2$$



      then refer to standard limit as $tto 0$



      $$frac1-cos tt^2to frac12$$






      share|cite|improve this answer
























        up vote
        2
        down vote













        HINT



        We have



        $$frac1-cos(ax^2+bx+c)(x-alpha)^2=frac1-cos[a(x-alpha)(x-beta)]a^2(x-alpha)^2(x-beta)^2a^2(x-beta)^2$$



        then refer to standard limit as $tto 0$



        $$frac1-cos tt^2to frac12$$






        share|cite|improve this answer






















          up vote
          2
          down vote










          up vote
          2
          down vote









          HINT



          We have



          $$frac1-cos(ax^2+bx+c)(x-alpha)^2=frac1-cos[a(x-alpha)(x-beta)]a^2(x-alpha)^2(x-beta)^2a^2(x-beta)^2$$



          then refer to standard limit as $tto 0$



          $$frac1-cos tt^2to frac12$$






          share|cite|improve this answer












          HINT



          We have



          $$frac1-cos(ax^2+bx+c)(x-alpha)^2=frac1-cos[a(x-alpha)(x-beta)]a^2(x-alpha)^2(x-beta)^2a^2(x-beta)^2$$



          then refer to standard limit as $tto 0$



          $$frac1-cos tt^2to frac12$$







          share|cite|improve this answer












          share|cite|improve this answer



          share|cite|improve this answer










          answered 1 hour ago









          gimusi

          72.3k73888




          72.3k73888




















              up vote
              2
              down vote













              Recall that $lim_t to 0 frac1-cos tt^2 = frac12$.



              We have



              $$frac1-cos(ax^2+bx+c)(x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)](x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)][a(x-alpha)(x-beta)]^2cdot a^2(x-beta)^2 xrightarrowxtoalpha frac12a^2(alpha-beta)^2$$






              share|cite|improve this answer
















              • 1




                @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
                – mechanodroid
                1 hour ago














              up vote
              2
              down vote













              Recall that $lim_t to 0 frac1-cos tt^2 = frac12$.



              We have



              $$frac1-cos(ax^2+bx+c)(x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)](x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)][a(x-alpha)(x-beta)]^2cdot a^2(x-beta)^2 xrightarrowxtoalpha frac12a^2(alpha-beta)^2$$






              share|cite|improve this answer
















              • 1




                @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
                – mechanodroid
                1 hour ago












              up vote
              2
              down vote










              up vote
              2
              down vote









              Recall that $lim_t to 0 frac1-cos tt^2 = frac12$.



              We have



              $$frac1-cos(ax^2+bx+c)(x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)](x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)][a(x-alpha)(x-beta)]^2cdot a^2(x-beta)^2 xrightarrowxtoalpha frac12a^2(alpha-beta)^2$$






              share|cite|improve this answer












              Recall that $lim_t to 0 frac1-cos tt^2 = frac12$.



              We have



              $$frac1-cos(ax^2+bx+c)(x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)](x-alpha)^2 = frac1-cos[a(x-alpha)(x-beta)][a(x-alpha)(x-beta)]^2cdot a^2(x-beta)^2 xrightarrowxtoalpha frac12a^2(alpha-beta)^2$$







              share|cite|improve this answer












              share|cite|improve this answer



              share|cite|improve this answer










              answered 1 hour ago









              mechanodroid

              24.2k52245




              24.2k52245







              • 1




                @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
                – mechanodroid
                1 hour ago












              • 1




                @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
                – mechanodroid
                1 hour ago







              1




              1




              @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
              – mechanodroid
              1 hour ago




              @MathOverview Yes. Check that $$ax^2+bx+ c = aleft(x - frac-b+sqrtb^2-4ac2aright)left(x - frac-b-sqrtb^2-4ac2aright)$$
              – mechanodroid
              1 hour ago










              up vote
              1
              down vote













              Hint. Use the Taylor series of
              $$
              cos(a(x-alpha)(x+beta))
              $$
              around $alpha$. That is
              $$
              cos(a(x-alpha)(x+beta))= 1-frac12(alpha-beta)^2(x-alpha)^2a^2+o((x-alpha)^3)
              $$






              share|cite|improve this answer


























                up vote
                1
                down vote













                Hint. Use the Taylor series of
                $$
                cos(a(x-alpha)(x+beta))
                $$
                around $alpha$. That is
                $$
                cos(a(x-alpha)(x+beta))= 1-frac12(alpha-beta)^2(x-alpha)^2a^2+o((x-alpha)^3)
                $$






                share|cite|improve this answer
























                  up vote
                  1
                  down vote










                  up vote
                  1
                  down vote









                  Hint. Use the Taylor series of
                  $$
                  cos(a(x-alpha)(x+beta))
                  $$
                  around $alpha$. That is
                  $$
                  cos(a(x-alpha)(x+beta))= 1-frac12(alpha-beta)^2(x-alpha)^2a^2+o((x-alpha)^3)
                  $$






                  share|cite|improve this answer














                  Hint. Use the Taylor series of
                  $$
                  cos(a(x-alpha)(x+beta))
                  $$
                  around $alpha$. That is
                  $$
                  cos(a(x-alpha)(x+beta))= 1-frac12(alpha-beta)^2(x-alpha)^2a^2+o((x-alpha)^3)
                  $$







                  share|cite|improve this answer














                  share|cite|improve this answer



                  share|cite|improve this answer








                  edited 1 hour ago

























                  answered 1 hour ago









                  MathOverview

                  8,34442962




                  8,34442962




















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