The graph of f(x) = 2x^3 + 6 x^2 - 90 x + 7 has two
horizontal tangents. One occurs at a negative value of x
and the other at a positive value of x .

What is the negative value ofx where a horizontal tangent occurs?

What is the positive value ofx where a horizontal tangent occurs?

What is the negative value of

What is the positive value of

You can earn partial credit on this problem.