# What is the equation of the line normal to #f(x)=7x ^3+9x^2 # at #x=-2#?

##### 1 Answer

Jul 1, 2016

See explanation

#### Explanation:

Gradient of the given equation is it differential

Thus

So the gradient of the line normal to it at this point is:

'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Let the point on the original curve be

Substitute these values into equation (1) to find

I will let you do that!