因式分解 (a-2b)的二次方-14(a-2b)+49

(a-2b)²-14(a-2b)+49
=(a-2b-7)²
（a²+1）²- 4a²
=(a²+1-2a)(a²+1+2a)
=(a-1)²(a+1)²
题目可能有误
已知（2x-y-1）²+√xy-2 =0 ,求4x^3y-4x^2y^2+xy^3
（2x-y-1）²+√xy-2 =0
（2x-y-1）²=0
2x-y=1
√xy-2 =0
xy=2
4x^3y-4x^2y^2+xy^3
=xy(4x^2-4xy+y^2)
=xy(2x-y)^2
=2*1^2
=2
x-y=4,则(2分之x的平方+y的平方)-xy 的值为
(x^2+y^2)/2-xy
=1/2(x^2+y^2-2xy)
=1/2(x-y)^2
=1/2*4^2
=1/2*16
=8

(a-2b)²-14(a-2b)+49
=（a-2b-7）(a-2b-7)
（a²+1）²- 4a²
=(a+1)(a+1)(a-1)(a-1)