f(x)= x²+4x-5 nilai minimum adalah?

Diket :
Fungsi parabola
x² + 4x - 5

a = 1
b = 4
c = -5

Nilai maksimum/minimumnya adalah
= D/(-4a)
= (b² - 4ac)/(-4a)
= (4² - 4.1.(-5)) / (-4.(1))
= (16 + 20) / (-4)
= 36 / (-4)
= -9