find the vertex of f(x) equals 5X squared plus 9X -7
the vertex os ax^2+bx+c is at x = -b/2a
So, here that would be x = -9/10
So the vertex is at (-9/10,-221/20)
Or, completing the square to get the vertex form of the parabola,
y = 5x^2 + 9x - 7
= 5(x^2 + 9/5) - 7/5
= 5(x^2 + 9/5 + (9/10)^2) - 7/5 - 5(9/10)^2
= 5(x + 9/5) - 221/20
So now just read off the vertex, as figured above.