Question

(3a+b)(___)=b²-9a²

Answer 1

(3a+b)(_b-3a__)=b²-9a²

长方形周长为20 两条邻长x y,满足2(x-y)-x²+2xy-y²-1=0

2(x-y)-x²+2xy-y²-1=0,则2(x-y)-(x-y)²-1=0

即-（(x-y)-1）²=0

设x为长.y为宽

x+y=10,x-y=1

x=5.5,y=4.5