Write the equation of the quadratic function with roots -1 and 1 and a vertex at (0, -3).

With roots at r1 and r2, the facotred form is
f(x)=a(x-r1)(x-r2) where a is a constnat
given
roots at x=-1 and 1

f(x)=a(x-(-1))(x-1)
f(x)=a(x+1)(x-1)
and
a point is (0,-3)
input that
-3=a(0+1)(0-1)
-3=a(1)(-1)
-3=-a
3=a

equation is
f(x)=3(x+1)(x-1)
or expanded
f(x)=3x²-3