# Quick C1 QuestionWatch

Thread starter 9 years ago
#1
For the curve C with equation y = x^4–8x^2+3, (srry cant put in latex as it changes it )

(a) find ,dy/dx(2)

The point A, on the curve C, has x-coordinate 1.

(b) Find an equation for the normal to C at A, giving your answer in the form ax + by + c = 0,
where a, b and c are integers.

I've done a) and was just wondering how I go about b). I know I need to work it's gradient but is it still the minus recipricol of the answer in a?
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9 years ago
#2
Using your answer from (a)
dy/dx = 4x^3 - 16x
Put in the x co-ordinate
At x=1 dy/dx = 4(1^3) - 16(1)
dy/dx = -12
This would give you the gradient for the tangent, so the gradient for the normal is 1/12

Then go on to work out the y co-ordinate for when x=1 and work out the equation of the line.
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Thread starter 9 years ago
#3
Ah thanks a lot, I see what I need to do.
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