vertex form of y=x^2-4x-9
complete the squarefirst isolate x termsy=(x^2-4x)-9complete square inside (take 1/2 of square of b )-4/2=-2, (-2)^2=4add 4-4 insidey=(x^2-4x+4-4)-9complete the squarey=((x-2)^2-4)-9y=(x-2)^2-4-9y=(x-2)^2-13
