已知:a=2x＾2-x+3,b=3x＾2+x-1.求:当x=1/2时2(3a-b)-3(b-3a)的值.
问题描述：
已知:a=2x＾2-x+3,b=3x＾2+x-1.求:当x=1/2时2(3a-b)-3(b-3a)的值.
答
2(3a-b)-3(b-3a)
=6a-2b-3b+9a
=15a-5b
=15(2x²-x+3)-5(3x²+x-1)
=30x²-15x+45-15x²-5x+5
=15x²-20x+50
=15/4-10+50
=175/4