Question

若x+y=3,xy=2,则(5x+2)-(3xy-5y)=_________

这题我不会，过程讲解写详细一点，尤其是讲解哦！

Answer 1

(5x+2)-(3xy-5y)=5x+2-3xy+5y(去括号）
=（5x+5y)-3xy+2
=5(x+y)-3xy+2
因为x+y=3,xy=2, 整体代入得
(5x+2)-(3xy-5y)=5(x+y)-3xy+2=5x3-3x2+2=15-6+2=9+2=11

Answer 2

(5x+2)-(3xy-5y)=5x+2-3xy+5y=5x+5y-3xy+2=5(x+y)-3xy+2
讲x+y=3,xy=2带入得:5x3-3x2+2=11