1-4x²
=1-(2x)²
=(1+2x)(1-2x)
（2a-b）²+9a²
=4a²-4ab+b²+9a²
=13a²-4ab+b²
题目有错
a²（x-y）+b²（y-x）
=a²（x-y）-b²（x-y）
=(x-y)(a²-b²)
=(x-y)(a+b)(a-b)
x²-y²+2x-2y
=(x+y)(x-y)+2(x-y)
=(x-y)(x+y+2)
x7次方-x
=x(x^6-1)
=x(x²-1)(x⁴+x²+1)
=x(x+1)(x-1)(x⁴+x²+1)
a³-4a
=a(a²-4)
=a(a+2)(a-2)