Thread: the equation of the normal to the curve

I already update the post, every one look it clear....refer to my post on no 10 & 11

here my problem
Determine the equation of the normal to the curve y = x^3-6x^2-2x which are perpendicular to the straight line 4-x+2y=0

just check my calculation..what wrong??

i already put the actual ans @ pg 2 of 2 at bottom

-----------------------------------------------
actual answers:

y + x + 12 = 0
or
27y + 27x + 4 = 0

pg 1 of 2

pg 2 of 2

sorry because it small in view...how to make it bigger size

just click on it to get the enlarged version

I would really like to help you!
But I simply cannot read that image!
Why don’t you simply retype the posting to make it readable?

Originally Posted by Plato

I would really like to help you!
But I simply cannot read that image!
Why don’t you simply retype the posting to make it readable?

tq for your response... i will try use image shack...sorry Mr Ploto...

i not very familiar to use math simbol here

thank for your help

pg 1 of 2
ImageShack - Hosting :: normalpg1sa8.png

pg 2 of 2

ImageShack - Hosting :: normalequation2ic6.jpg

Originally Posted by nikk

I already update the post, every one look it clear....refer to my post on no 10 & 11

here my problem
Determine the equation of the normal to the curve y = x^3-6x^2-2x which are perpendicular to the straight line 4-x+2y=0

just check my calculation..what wrong??

i already put the actual ans @ pg 2 of 2 at bottom

-----------------------------------------------
actual answers:

y + x + 12 = 0
or
27y + 27x + 4 = 0

If those are the answers then the question is wrong.

1. The lines in the answers are NOT perpendicular to the line 4 - x + 2y = 0.

2. Furthermore, since the gradient of the lines in the answer is m = -1, the tangent to the cubic must have gradient m = 1. Solving 3x^2 - 12x -2 = 1 does not give an integer solution for x and therefore cannot lead to the answers.

Re-check the question. If the question is as you say, then the question is wrong. There's nothing more can be done.

Originally Posted by mr fantastic

If those are the answers then the question is wrong.

1. The lines in the answers are NOT perpendicular to the line 4 - x + 2y = 0.

2. Furthermore, since the gradient of the lines in the answer is m = -1, the tangent to the cubic must have gradient m = 1. Solving 3x^2 - 12x -2 = 1 does not give an integer solution for x and therefore cannot lead to the answers.

Re-check the question. If the question is as you say, then the question is wrong. There's nothing more can be done.

tq for your reply sir..do u think my ans is correct....

Originally Posted by nikk

tq for your reply sir..do u think my ans is correct....

I can't see any obvious mistakes.

Originally Posted by mr fantastic

I can't see any obvious mistakes.

tq for your support