Thread: Just a little question i need help with.

1. The curve C is given by the equation y=mx³-x²+8x+2, for a constant m
A) find dy/dx

The point P lies on C, and has the x-value 5
The normal to C at P is parallel to the line given by the equation y+4x-3=0.

B)find the gradient of the curve at C at P.

Hence find:
C) (I) the value of m,

(ii) the y-value at p.

For A) i got:
dy/dx=3mx²-x+8


I'm not really sure how to carry on with it now any help would be brilliant
Thanks.

a) Check your differentiation. Your second term is wrong.

b) Evaluate

c) The statement "The normal to C at P is parallel to the line given by the equation y+4x-3=0" tells us that the derivative of y with respect to x at x = 5 is the negative reciprocal of the slope of the given line. So, find the slope of the line , invert it, negate it and equate this to .

i) Solve the resulting equation for .

ii) We are told the xcoordinate of point P is 5, so to find the y-coordinate evaluate .

Thanks i was really stuck on that question