4m²-n²=(2m+n)(2m-n)0.81a²-0.04b²=(0.9a+0.2b)(0.9a-0.2b)2x²-8=2(x²-4)=2(x+2)(x-2)a-a三次方=a(1-a²)=a(1+a)(1-a)1-x四次方=(1+x²)(1-x²)=(1+x²)(1+x)(1-x)...