作业帮若x=-2,求3x²-[7x²-2（x²-3x）-2x]的值.老师让的没办法啊
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若x=-2,求3x²-[7x²-2（x²-3x）-2x]的值.老师让的没办法啊
若x=-2,求3x²-[7x²-2（x²-3x）-2x]的值.
老师让的没办法啊
若x=-2,求3x²-[7x²-2（x²-3x）-2x]的值.老师让的没办法啊
原式=3x²-(7x²-2x²+6x-2x)
=3x²-(5x²+4x)
=3x²-5x²-4x
=-2x²-4x
=-2×4-4×(-2)
=-8+8
=0