Find the equation of the tangent and the normal at the given point for:
f(x)=x^2, (2,4)
at x=2
- f(x)=2^2=4 gradient is =4
y=mx+c
y=4x+c (2,4)
4=4*2+c c=-4
- y=4x-4
but I don't know how to do normal?....thx
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asked Aug 25, 2011 at 12:13
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2$\begingroup$ If order is given, then no answer is written. $\endgroup$– DidAug 25, 2011 at 12:16
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$\begingroup$ sorry, what do you mean by that? $\endgroup$– Cin Sb SangpiAug 25, 2011 at 12:21
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1$\begingroup$ 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. $\endgroup$– jorikiAug 25, 2011 at 12:26
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1$\begingroup$ 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? $\endgroup$– Gerry MyersonAug 25, 2011 at 12:27
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$\begingroup$ 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. $\endgroup$– Cin Sb SangpiAug 25, 2011 at 12:30
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1 Answer
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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.
answered Aug 25, 2011 at 12:52
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$\begingroup$ thx for that, I can't vote sorry..my point very low! $\endgroup$ Aug 25, 2011 at 12:56
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