Question 122112
let x="length of longest rectangle", y="width of longest rectangle) __ xy=480 __ y=480/x


(x-10)(y+4)=xy __ xy-10y+4x-40=xy __ -10y+4x-40=0


substituting __ -10(480/x)+4x-40=0


multiplying by x __ -4800+4x^2-40x=0 __ dividing by 4 __ x^2-10x-1200=0


factoring __ (x-40)(x+30)=0