f(x) = (x -
)² -
the equation of a quadratic in vertex form is
y = a(x - h)² + k
where (h, k) are the coordinates of the vertex and a is a multiplier
given a quadratic in standard form : y = ax² + bx + c ( a ≠ 0 )
then the x- coordinate of the vertex is
= -
f(x) = x² - 11x + 9 is in standard form
with a = 1, b = - 11 and c = 9
= -
=
substitute this value into the equation for y- coordinate
y = (
)² - 11(
) + 9
=
-
+
= -
f(x) = (x -
)² -
← in vertex form