the graph of f(x)=2x^3+15x^2-84x+13 has two horizontal tangents. one occurs at a negative value of x and the other at a positive value of x.

what is the positive and negative values of X

Question

the graph of f(x)=2x^3+15x^2-84x+13 has two horizontal tangents. one occurs at a negative value of x and the other at a positive value of x.

what is the positive and negative values of X

mertsj · Answer

Well, if the tangent is horizontal, that means that its slope is 0.  Also the first derivative is the slope function so I guess I would want to know when the first derivative is equal to 0

anonymous · Answer

so the first derivitve is 6x^2+15x-84

mertsj · Answer

No.  6x^2+30x-84

anonymous · Answer

opps thats what i meant... what do you do next

mertsj · Answer

We want to know when the slope is 0 so set the slope function equal to 0 and solve the quadratic equation.

anonymous · Answer

we get 6*(x-2)(x+7) ?

anonymous · Answer

i got it thanks!

mertsj · Answer

Excellent!!  And you're welcome.