(x²-1)(x+3)(x+5)+12.
=(X+1)(X-1)(x+3)(x+5)+12.
=(x²+4X+3)(X²+4X-5)+12
=(x²+4X+3)²-8(x²+4X+3)+12
=(x²+4X+3-2)(x²+4X+3-6)
=(x²+4X+1)(x²+4X-3)
(x²-1)(x+3)(x+5)+12.
=(X+1)(X-1)(x+3)(x+5)+12.
=(x²+4X+3)(X²+4X-5)+12
=(x²+4X+3)²-8(x²+4X+3)+12
=(x²+4X+3-2)(x²+4X+3-6)
=(x²+4X+1)(x²+4X-3)