5x²-3xy-4y²-11xy-7x²＋2y²
=5x²-7x²＋2y²-4y²-3xy-11xy
=-2x²-2y²-14xy
=-2(x²+y²)-14xy
=-2*7-14*(-2)
=-14+28
=14我怎么看不懂