先化简再求值 5a²-[a²-(2a-5a²)-2(a²-3a)] 其中a=4.
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![先化简再求值 5a²-[a²-(2a-5a²)-2(a²-3a)] 其中a=4.](/uploads/image/z/1963426-58-6.jpg?t=%E5%85%88%E5%8C%96%E7%AE%80%E5%86%8D%E6%B1%82%E5%80%BC+5a%26%23178%3B-%5Ba%26%23178%3B-%282a-5a%26%23178%3B%29-2%28a%26%23178%3B-3a%29%5D+%E5%85%B6%E4%B8%ADa%3D4.)
先化简再求值 5a²-[a²-(2a-5a²)-2(a²-3a)] 其中a=4.
先化简再求值 5a²-[a²-(2a-5a²)-2(a²-3a)] 其中a=4.
先化简再求值 5a²-[a²-(2a-5a²)-2(a²-3a)] 其中a=4.
5a^2-(a^2-2a+5a^2-2a^2+6a)=5a^2-(4a^2+4a)=5a^2-4a^2-4a=a^2-4a
a=4 a^2-4a=4^2-4x4=0
原式=5a²-(a²-2a+5a²-2a²+6a)=5a²-(4a²+4a)=a²-4a
当a=4时,原式=0