Explanation:
a quadratic equation has 2 zeros.
luckily we got 2 points with y = 0, so these define the zero points.
a quadratic function is usually looking like
ax² + bx + c = 0
and with the zeros being the factors, we get
y = a(x - z1)(x - z2) = a(x + 4)(x - 2) =
= a(x² - 2x + 4x - 8) = a(x² + 2x - 8)
to get "a" we use the third point.
-2 = a((-2)² + 2×-2 - 8) = a(4 - 4 - 8) = -8a
a = -2/-8 = 1/4
and the equation is
y = (1/4)x² + (1/2)x - 8/4 = (1/4)x² + (1/2)x - 2