Answer:

x² + 8x + 15 = 0

x² + 8x = -15

x² + 8x + 16 = -15 + 16

(x + 4)² = 1

√(x + 4)² = √1

x + 4 = ±1

x + 4 = -1

x = -1 - 4

x = -5

x + 4 = 1

x = 1 - 4

x = -3