解
x²-4xy+4y²=(x-2y)²
1-8x+16x²=(1-4x)²
(1/2x-3y)²=1/4x²-3xy+9y²
(3m-2n)²=9m²-12mn+4n²
4m²-4mn+n²=(2m-n)²
3x²-7x+2=(3x-1)(x-2)