x-y=3,xy=5,求代数式(7xy+4x-7y)+(6x-3xy)-(3y+4xy)的值快

问题描述:

x-y=3,xy=5,求代数式(7xy+4x-7y)+(6x-3xy)-(3y+4xy)的值

7×5+4x-7y+6x-3×5-3y+4×5=10*3=30

(7xy+4x-7y)+(6x-3xy)-(3y+4xy)=7xy+4x-7y+6x-3xy-3y-4xy=10x-10y=10(x-y)=10*3=30