先化简(3x²-4y²)+[-(x²-2xy-y²)]-[-(3x²-2xy-y²)] 再求值,其中x=-1 y=-2

问题描述:

先化简(3x²-4y²)+[-(x²-2xy-y²)]-[-(3x²-2xy-y²)] 再求值,其中x=-1 y=-2

原式=3x²-4y²-x²+2xy+y²+3x²-2xy-y²
=5x²-4y²
=5*1-4*4
=-11

(3x²-4y²)+[-(x²-2xy-y²)]-[-(3x²-2xy-y²)]=3x²-4y²-x²+2xy+y²+3x²-2xy-y²=5x²-4y²=5x(-1)²-4x(-2)²=5-16=-11如果本题有什么不明...