Find the equation of the line?

**mj.alawami** · November 26th 2009, 01:55 AM

Question:
FInd the equation of the normal lines to the curve $y=x^3-3x$ which is parallel to the line of $2x+18y-9=0$

Attempt:
$f'(x)=3x^2-3$
$m=9$
$x=2 ;y=2$
$y-2=9(x-2)$

Is my equation correct?
If not please answer in steps
Thank you

**mathaddict** · November 26th 2009, 02:04 AM

Originally Posted by mj.alawami

Question:
FInd the equation of the normal lines to the curve $y=x^3-3x$ which is parallel to the line of $2x+18y-9=0$

Attempt:
$f'(x)=3x^2-3$
$m=9$
$x=2 ;y=2$
$y-2=9(x-2)$

Is my equation correct?
If not please answer in steps
Thank you

HI

$y=x^3-3x\Rightarrow \frac{dy}{dx}=3x^2-3$

This is the gradient of tangent . The gradient of normal would be perpendicular to it .

Gradient of normal , call it M2 is $-\frac{1}{9}$ (do u know y)

$(3x^2-3)(M2)=-1$

$-\frac{1}{9}=-\frac{1}{3x^2-3}$

solving this ... $x=\pm 2$

Put this into the original equation (curve) to find the y's .

Math Help - Find the equation of the line?

LinkBack

Thread Tools

Display

Find the equation of the line?

Similar Math Help Forum Discussions

Find an Equation of the Tangent Line to the parabola at the given point and find....

To find the equation of a line given it is contained in a plane and cuts another line

Find equation of line f(x) parallel to given line

Find the equation of a line perpendicular to a line with a given equation

the equation of a straight line is 3x+2y=11. find the equation of a parrallel line pa

Search Tags