(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 )