Question

Consider the quadratic function:
f(x) = x2 – 8x – 9

Vertex:
What is the vertex of the function?

Answer 1

f(x)=x^2 - 4x - 4x +16-16-9
=x(x - 4) -4(x - 4) - 25
= (x-4)(x-4) -25
f(x)=(x-4)^2 - 25
the vertex is (4, -25)
the vertex occur at
x = - b/2a and y = (4ac - b^2)/4a
x= - - 8/(2*1)=4
y=[4*1*(-9) - (-8)^2]/(4*1)
= (-36-64)/4 = - 100/4 = - 25

Answer 2

the answer is ( 4 , - 25 )

:)