已知:a+b=3X²-5X+4,a-c=3X²+2X-5.求:当X=4,b+c的值

已知:a+b=3X²-5X+4,a-c=3X²+2X-5.求:当X=4,b+c的值
已知:a+b=3X²-5X+4,a-c=3X²+2X-5.求:当X=4,b+c的值

已知:a+b=3X²-5X+4,a-c=3X²+2X-5.求:当X=4,b+c的值
b+c=(a+b)-(a-c)
=3x²-5x+4-3x²-2x+5
=-7x+9
当x=4时
b+c=-28+9
=-19

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