Explanation:
as the formula says for the acid of symmetry :
x = -b/2a
in the function m(x) = 2x² + 8x +3
we have
a = 2
b = 8
c = 3
the axis of symmetry is
x = -8/(2×2) = -8/4 = -2
the vertex is (h, k) out of the form
m(x) = a(x - h)² + k
we know already, a = 2
for the rest we do all the multiplications and then we compare it with the original function :
m(x) = a(x² - 2hx + h²) + k = ax² - 2ahx + ah² + k
a = 2
-2ah = 8
-2×2×h = 8
-4h = 8
h = -2
ah² + k = 3
2×(-2)² + k = 3
8 + k = 3
k = -5
so, the vertex is (-2, -5)