(2Х +7Y)*( 2X - Y) = 4X^2 - 2XY + 14XY - 7Y^2 = 4X^2 + 12XY - 7Y^2 ====================================================- 7Y * ( 2X - Y) = - 14XY + 7Y^2 =====================================================4X^2 + 12XY - 7Y^2 - 14XY + 7Y^2 = 4X^2 - 2XY ======================================================4X^2 - 2XY ( Ответ )