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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. – Did Aug 25 '11 at 12:16
sorry, what do you mean by that? – Sb Sangpi Aug 25 '11 at 12:21
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. – joriki Aug 25 '11 at 12:26
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? – Gerry Myerson Aug 25 '11 at 12:27
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. – Sb Sangpi Aug 25 '11 at 12:30
up vote 1 down vote accepted

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 point very low! – Sb Sangpi Aug 25 '11 at 12:56
@Sb: But you can accept an answer if it answers your question. – joriki Aug 25 '11 at 13:01
aww..i see now..thx for that! – Sb Sangpi Aug 25 '11 at 13:07

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