题目

多项式的乘法,
1.(2X-Y)(X+3Y) 3.(xy+1)(2xy+3) 2.(2x-5y)(-2x-5y) 4.5(x-1)(x+3)-2(x-5)(x-2) 5.先化简,再求值(x+3)(x-3)-x(x-6).其中X=2
6.5Z(1-2x)+(x+1)(10x-2),其中X=-13/2

提问时间：2020-11-18

答案

1.(2X-Y)(X+3Y)
=2X²+6XY-XY-3Y²
=2X²+5XY-3Y²
2.(2x-5y)(-2x-5y)
=-4X²-10XY+10XY+25Y²
=25Y²-4X²
3.(xy+1)(2xy+3)
=2X²Y²+3XY+2XY+3
=2X²Y²+5XY+3
4.5(x-1)(x+3)-2(x-5)(x-2)
=5(X²＋3X-X-3)-2(X²-2X-5X+10)
=5X²＋10X-15-2X²+14X-20
=3X²+24X-35
5.先化简,再求值(x+3)(x-3)-x(x-6).其中X=2
(x+3)(x-3)-x(x-6)
=X²-9-X²+6X
=-9+12
=3
6.5Z(1-2x)+(x+1)(10x-2),其中X=-13/2
=5Z-10XZ+10X²-2X+10X-2
=5Z-10XZ+10X²+8X-2
=5Z-10(-13/2)Z+10(-13/2)²+8(-13/2)-2
=5Z+65Z+845-52-2
=70Z+845/2-54
=70Z+737/2