（x+y)(2p-q)-2(y+x)(2q-p)
=（x+y)(2p-q-2(2q-p))
=(x+y)(4p-5q)
5m(x-y)(a-b+c)-6n(y-x)(a-b+c)
=5m(x-y)(a-b+c)+6n(x-y)(a-b+c)
=(5m+6n)(x-y)(a-b+c)