Which equation is y = 9x2 + 9x - 1 rewritten in vertex form?

The general equation of a quadratic is expressed as y = ax^2+bx+c. To convert the general equation to vertex form, we need to obtain this form:

(y - k) = a (x - h) ^2

This could be done by using completing the square method.

y = 9x^2 + 9x - 1 y + 1 = 9 (x^2 + x)

y + 1 + 9/4 = 9 (x^2 + x + 1/4)

y + 13/4 = 9 (x+1/2) ^2