Step-by-step explanation:
just try the values.
and remember the vertex of a parabola
ax² + bx + c = 0
x value of the vertex = -b/2a
in our case
a = 1
b = -4
c = -21
x-vertex = - -4/(2×1) = 4/2 = 2
y-vertex = 2² - 4×2 - 21 = 4 - 8 - 21 = -25
C is correct
about the 0s :
there is only one option with x = -3. so, let's try this first :
0 = (-3)² - 4×-3 - 21 = 9 + 12 - 21 = 0
so, A is correct
