作业帮5a²+[a²+（5a²-2a）-2(a²-3a）]其中a=-1/2 先化简再求值1/2（x²-y²)-4(2x²-3y²）其中x=-3y=2
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![5a²+[a²+（5a²-2a）-2(a²-3a）]其中a=-1/2 先化简再求值1/2（x²-y²)-4(2x²-3y²）其中x=-3y=2](/uploads/image/z/746244-36-4.jpg?t=5a%26%23178%3B%2B%5Ba%26%23178%3B%2B%EF%BC%885a%26%23178%3B-2a%EF%BC%89-2%28a%26%23178%3B-3a%EF%BC%89%5D%E5%85%B6%E4%B8%ADa%3D-1%2F2+%E5%85%88%E5%8C%96%E7%AE%80%E5%86%8D%E6%B1%82%E5%80%BC1%2F2%EF%BC%88x%26%23178%3B-y%26%23178%3B%29-4%282x%26%23178%3B-3y%26%23178%3B%EF%BC%89%E5%85%B6%E4%B8%ADx%3D-3y%3D2)
5a²+[a²+（5a²-2a）-2(a²-3a）]其中a=-1/2 先化简再求值1/2（x²-y²)-4(2x²-3y²）其中x=-3y=2
5a²+[a²+（5a²-2a）-2(a²-3a）]其中a=-1/2 先化简再求值
1/2（x²-y²)-4(2x²-3y²）其中x=-3y=2
5a²+[a²+（5a²-2a）-2(a²-3a）]其中a=-1/2 先化简再求值1/2（x²-y²)-4(2x²-3y²）其中x=-3y=2
5a²+[a²+（5a²-2a）-2(a²-3a）]
=5a²+[a²+5a²-2a-2a²+6a]
=5a²+[4a²+4a]
=5a²+4a²+4a
=9a²+4a
代入：a=-1/2
9a²+4a=9（-1/2）²-2=9/4-2=1/2