Question

What is the x coordinate of the vertex of the parabola whose equation is y=3x^2+9x?

A. -3
B. -1 and a half
C. -2/3

Answer 1

Find the vertex by setting the 1st derivative to 0
1st derivative is y=6x+9.

6x+9=0 => x=-9/6 = -3/2

So B is the answer.