aska2k1
幼苗
共回答了13个问题采纳率:92.3% 举报
解
(3x²-2x+1)(x+b)
=x(3x²-2x+1)+b(3x²-2x+1)
=3x³+(-2x²+3bx²)+(x-2bx)+b
=3x³+(3b-2)x²+(1-2b)x+b
不含x²
∴3b-2=0,
∴b=2/3
(x-y)(x-2y)-0.5(2x-3y)(x+2y)
=(x²-3xy+2y²)-0.5(2x²+xy-6y²)
=(x²-x²)+(-3xy-0.5xy)+(2y²+3y²)
=-3.5xy+5y²
=-3.5×2×0.4+5×0.4²
=0.8-2.8
=-2
1年前
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