Answer
Vertex: $(1,-16)$
Opens upward
x-intercepts: -3, 5
y-intercept: -15
Work Step by Step
$f(x)=x^2-2x-15$
$y=x^2-2x-15$
$y=x^2-2x-15+(-2/2)^2-(-2/2)^2$
$y=x^2-2x-15+(-1)^2-(-1)^2$
$y=x^2-2x-15+1-1$
$y=x^2-2x+1-16$
$y=(x-1)^2-16$
Vertex: $(1,-16)$
Opens upward
$x=0$
$f(x)=x^2-2x-15$
$f(0)=0^2-2*0-15$
$f(0)=0-0-15$
$f(0)=-15$
$y=0$
$y=(x-1)^2-16$
$y+16=(x-1)^2-16+16$
$y+16=(x-1)^2$
$0+16=(x-1)^2$
$16=(x-1)^2$
$\sqrt {16}=\sqrt {(x-1)^2}$
$±4 = x-1$
$4=x-1$
$4+1=x-1+1$
$5=x$
$-4=x-1$
$-4+1=x-1+1$
$-3=x$
x-intercepts: -3, 5
y-intercept: -15
