Giúp e bài 1+2 giải từng ý

Bài `1:`

`a)1/3x. (-3/5x^3)`

`=-1/5x^4`

`b)y^2(2/7y^3-2y^2+1/2)`

`=y^2. 2/7y^3-y^2. 2y^2+y^2. 1/2`

`=2/7y^5-2y^4+1/2y^2`

`c)(x-1/2)(x^2+2x-1/2)`

`=x.x^2+x.2x-x. 1/2-1/2. x^2-1/2. 2x-1/2.(-1/2)`

`=x^3+2x^2-1/2x-1/2x^2-x+1/4`

`=x^3+(2x^2-1/2x^2)-(1/2x+x)+1/4`

`=x^3+3/2x^2-3/2x+1/4`

Bài `2:`

`a)`

`A(x)=x^3-x^2+7x-x^2-1`

`=x^3-(x^2+x^2)+7x-1`

`=x^3-2x^2+7x-1`

`B(x)=3x^3-2x^2-x-1-2x^3`

`=(3x^3-2x^3)-2x^2-x-1`

`=x^3-2x^2-x-1`

`b)`

`A(x)+B(x)=(x^3-2x^2+7x-1)+(x^3-2x^2-x-1)`

`=x^3-2x^2+7x-1+x^3-2x^2-x-1`

`=(x^3+x^3)-(2x^2+2x^2)+(7x-x)-(1+1)`

`=2x^3-4x^2+6x-2`

`A(x)-B(x)=(x^3-2x^2+7x-1)-(x^3-2x^2-x-1)`

`=x^3-2x^2+7x-1-x^3+2x^2+x+1`

`=(x^3-x^3)-(2x^2-2x^2)+(7x+x)-(1-1)`

`=8x`

`c)`

Thay `x=-1` vào biểu thức `A(x)+B(x)` ta được:

`A(-1)+B(-1)=2.(-1)^3-4.(-1)^2+6.(-1)-2`

`=2.(-1)-4.1-6-2`

`=-2-4-8`

`=-14`