# What is the equation of the normal line of #f(x)=x^3 + 3x^2 + 7x - 1 # at #x=-1 #?

##### 1 Answer

Aug 29, 2016

#### Explanation:

The gradient function is the first derivative

So the gradient when X=-1 is 3-6+7=4

The gradient of the normal , perpendicular, to the tangent is

If you are not sure about this draw a line with gradient 4 on squared paper and draw the perpendicular.

So the normal is

But this line goes through the point (-1,y)

From original equation when X=-1 y=-1+3-7-1=6

So 6=