(x+1)(x-1)(x+3)(x+5)+16 =(x+1)(x+3)(x-1)(x+5)+16 =(xx+4x+3)(xx+4x-5)+16 =(xx+4x)^2-2(xx+4x)-15+16 =(xx+4x)^2-2(xx+4x)+1=(xx+4x-1)^2 注：(x+1)(x+3)=xx+4x+3 (x-1)(x+5)=xx+4x-5