81(x+y)²-121(m+n)² =(9x+9y-11m-11n)(9x+9y+11m+11n)
(x²+y²)²-x²y² =(x²+xy+y²)(x²-xy+y²)
(2m-n)²-(3m+2n)²=(2m-n+3m+2n)(2m-n-3m-2n)=-(5m+n) (m+3n)
81(x+y)²-121(m+n)² =(9x+9y-11m-11n)(9x+9y+11m+11n)
(x²+y²)²-x²y² =(x²+xy+y²)(x²-xy+y²)
(2m-n)²-(3m+2n)²=(2m-n+3m+2n)(2m-n-3m-2n)=-(5m+n) (m+3n)