Question

y(y+2x)-(x+y) в квадрате

Answer 1

$y(y+2x)- (x+y)^{2} = y^{2} +2xy-( x^{2} +2xy+ y^{2} )$
$= y^{2} +2xy- x^{2} -2xy- y^{2} =- x^{2}$