解题思路:(1)可将x2+y2=7,xy=-2看做一个方程组求出x,y的值,再代入7x2-3xy-2y2-11xy-5x2+4y2求值;
(2)将(x2+y2)和xy分别看做一个整体求解.
∵x2+y2=7,xy=-2,
∴7x2-3xy-2y2-11xy-5x2+4y2,
=(7x2-5x2)+(4y2-2y2)-(3xy+11xy),
=2x2+2y2-14xy,
=2(x2+y2)-14xy,
=2×7-14×(-2),
=14+28=42.
点评:
本题考点: 整式的混合运算—化简求值.
考点点评: 解答此题需要先化简,即先合并同类项,然后应用整体思想求值.