3a^2-[7a^2-2a-3(a^2-a)+1]先去括号,再合并同类项
3a^2-[7a^2-2a-3(a^2-a)+1]
=3a^2-[7a^2-2a-3a^2+3a+1]
=3a^2-7a^2+2a+3a^2-3a-1
=-a^2-a-1
3a²-[7a²-2a-3(a²-a)+1]
=3a²-7a²+2a+3(a²-a)-1
=3a²-7a²+2a+3a²-3a-1
=(3a²-7a²+3a²)+(2a-3a)-1
=(3-7+3)a²+(2-3)a-1
=-a²-a-1
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