1、计算:①(4X²-5xy)-(1/3y²+2x²)+2(5xy-1/4y²-1/12y²)2、先化简,再求值:①(2a²-b)-(a²-4b)-(b+c),其中a=1/3,b=1/2,c=1②2(x的立方-2y²)-(x-2y)-(x-3y²+2x的立方),其中X=-3,y=-2

问题描述:

1、计算:
①(4X²-5xy)-(1/3y²+2x²)+2(5xy-1/4y²-1/12y²)
2、先化简,再求值:
①(2a²-b)-(a²-4b)-(b+c),其中a=1/3,b=1/2,c=1
②2(x的立方-2y²)-(x-2y)-(x-3y²+2x的立方),其中X=-3,y=-2

1.
2x^2+5xy-y^2
2.
a^2+2b-c 1/9
-y^2-2x+2y -2

1、计算
①(4X²-5xy)-(1/3y²+2x²)+2(5xy-1/4y²-1/12y²)
=4x^2-5xy-1/2y^2-2x^2+10xy-1/2y^2-1/6y^2
=4x^2-2x^2+10xy-5xy-1/2y^2-1/3y^2-1/6y^2
=2x^2+5xy-y^2
2、先化简,再求值:
①(2a²-b)-(a²-4b)-(b+c),其中a=1/3,b=1/2,c=1
=2a^2-b-a^2+4b-b-c
=a^2+2b-c
=(1/3)^2+2*1/2-1
=1/9+1-1
=1/9
②2(x的立方-2y²)-(x-2y)-(x-3y²+2x的立方),其中X=-3,y=-2
=x^3-2y^2-x+2y-x+3y^2-2x^3
=-x^3+y^2-2x+2y
=-(-3)^3+(-2)^2-2*(-3)+2*(-2)
=-27+4+6-4
=-21