2 ways:
1. hackway
2. convert to vertex form
hack way is
for
y=ax^2+bx+c
the x value of the vertex is -b/2a
plug that value in to get y value
y=-5x^2-10x-13
a=-5
b=-10
xvaluevertex=-(-10)/(2*-5)=10/-10=-1
xvalue=-1
sub back
y=-5(-1)^2-10(-1)-13
y=-5(1)+10-13
y=-5+10-13
y=-8
xvalue=-1
yvalue=-8
vertex=(-1,-8)
or convert to y=a(x-h)^2+k where (h,k) is vertex
y=-5(x^2+2x)-13
y=-5(x^2+2x+1-1)-13
y=-5((x+1)^2-1)-13
y=-5(x+1)^2+5-13
y=-5(x+1)^2-8
y=-5(x-(-1))^2+(-8)
vertex is (-1,-8)