x³-9x=?16x四次方-1=?6xy²-9x²y-y³=?（2a-b)&su

x³-9x=X(X^2-9) =X(X+3)(X-3)
16x^4-1=(4X^2)^2-1=(4X^2+1)(4X^2-1)==(4X^2+1)(2X+1)(2X-1)
6xy²-9x²y-y³=Y(6XY-9X^2-Y^2)=-Y(9X^2-6XY+Y^2)=-Y(3X-Y)^2
(2a-b)²+8ab=4a^2-4ab+b^2+8ab=4a^2+4ab+b^2=(2a+b)^2