先化簡,再求值:-2x2-2[3y2-2(x2-y2)+6],其中x=-1,y=-2.
問題詳情:
先化簡,再求值:-2x2-2[3y2-2(x2- y2)+6],其中x=-1,y=-2.
【回答】
-2x2-2[3y2-2(x2-y2)+6]
=-2x2-2[3y2-2x2 + 2y2+6]································································· 3分
=-2x2-6y2 + 4x2 -4y2-12···································································· 4分
=2x2-10y2 -12 ····················································································· 5分
當x=-1,y=-2時
原式=2×(-1)2-10×(-2)2-12
=2×1-10×4-12
=2-40-12
=-50······································································································· 6分
知識點:整式的加減
題型:解答題
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