Just need a little help on these questions. :)

• Nov 12th 2012, 02:01 PM
Walshy4119
Just need a little help on these questions. :)
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.

Just really stuck on this question any help would be brilliant :)
Thanks.
• Nov 12th 2012, 03:47 PM
skeeter
Re: Just need a little help on these questions. :)
please post calculus problems in the calculus forum ... the lobby is for introductions.
• Nov 12th 2012, 04:32 PM
HallsofIvy
Re: Just need a little help on these questions. :)
Quote:

Originally Posted by Walshy4119
1. The curve C is given by the equation y=mx3-x2+8x+2, for a constant m
A) find dy/dx

Okay, what did you get for dy/dx?

Quote:

The point P lies on C, and has the x-value 5
So what are y and dy/dx when x= 5?

Quote:

The normal to C at P is parallel to the line given by the equation y+4x-3=0.
Are you asked to find m so that this is true? The slope of a line perpendicular to a curve, y= f(x), is equal to $-1/f'(x)$. What is the slope of the line y+ 4x- 3= 0?

Quote:

Find the gradient of the curve at C at P.
Okay, that is dy/dx evaluated at x= 5.

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

(ii) the y-value at p.

Just really stuck on this question any help would be brilliant :)
Thanks.[/QUOTE]
• Nov 13th 2012, 12:54 AM
Walshy4119
Re: Just need a little help on these questions. :)
Sorry i posted on the wrong page I'll post it properly now.