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Find the equation of the tangent and the normal at the given point for:

  1. f(x)=x^2, (2,4)

  2. at x=2

    • f(x)=2^2=4 gradient is =4
  3. y=mx+c

  4. y=4x+c (2,4)

  5. 4=4*2+c c=-4

  6. y=4x-4

but I don't know how to do normal?....thx

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    If order is given, then no answer is written.2011-08-25
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    sorry, what do you mean by that?2011-08-25
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    He means that a lot of people here don't take kindly to questions being "asked" in the imperative mode and your chances of getting an answer will increase significantly if you formulate your question as a question.2011-08-25
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    It means, some of us liked to be asked a question, rather than being given an order. It might also mean, what work have you put into this problem, other than copying it out from your homework assignment. What do you know about tangent lines and normal lines? What can *you* contribute here?2011-08-25
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    aww,,ok. Sorry for that. I'm in trouble with my homework. no one teach me, so I come here for help! thx for explains.2011-08-25
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    Have you read the [FAQ](http://math.stackexchange.com/faq)?2011-08-25
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    yes! especially (answer site for people studying math at any level and professionals in related fields.)2011-08-25
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    Hint: You know the slope (gradient) of the tangent. What is the slope of the normal?2011-08-25
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    As for the question, you should be taking derivatives. The slope of the tangent at x = a is f'(a). The normal slope is -1/f'(a)2011-08-25
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    thx for that, I can't vote sorry..my point very low!2011-08-25
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    @Sb: you like that MSE is an *answer site for people studying math at any level and professionals in related fields* and so do I. But MSE also asks: **Do your homework** *Have you thoroughly searched for an answer before asking your question? Sharing your research helps everyone. Tell us what you found and why it didn’t meet your needs. This demonstrates that you’ve taken the time to try to help yourself, it saves us from reiterating obvious answers, and most of all it helps you get a more specific and relevant answer!* The rest is here: http://math.stackexchange.com/questions/how-to-ask2011-08-25
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    thx for that! appreciate it! ;)2011-08-25

1 Answers 1

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Hint: The slope of the tangent times the slope of the normal is $-1$. You have a slope and a point on the tangent.

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    thx for that, I can't vote sorry..my point very low!2011-08-25
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    aww..i see now..thx for that!2011-08-25