Question

[Khánh Chi Nguyễn]

Cho đa thức: A(x)=3x^4-3/4x^3+2x^2-3 ; B(x)=8x^4+1/5x^3-9x+2/5; Tính : a, A(x)+ B(x); b, A(x)-B(x); c, B(x)-A(x).

Answer 1

[『Kuroba ム Tsuki Ryoo ︵²ᵏ⁷』]

`@` `\text {Đáp án}`

`\downarrow`

`a,`

`A(x)+B(x)=`\(\left(3x^4-\dfrac{3}{4}x^3+2x^2-3\right)+8x^4+\dfrac{1}{5}x^3-9x+\dfrac{2}{5}\)

`= 3x^4-3/4x^3+2x^2-3+8x^4+1/5x^3-9x+2/5`

`= (3x^4+8x^4)+(-3/4x^3+1/5x^3)+2x^2-9x+(-3+2/5)`

`= 11x^4-11/20x^3+2x^2-9x-13/5`

`b,`

`A(x)-B(x)=`\(3x^4-\dfrac{3}{4}x^3+2x^2-3-\left(8x^4+\dfrac{1}{5}x^3-9x+\dfrac{2}{5}\right)\)

`=3x^4-3/4x^3+2x^2-3-8x^4-1/5x^3+9x-2/5`

`= (3x^4-8x^4)+(-3/4x^3-1/5x^3)+2x^2+9x+(-3-2/5)`

`= -5x^4 -19/20x^3+2x^2+9x-17/5`

`c,`

`B(x)-A(x)=`\(8x^4+\dfrac{1}{5}x^3-9x+\dfrac{2}{5}-\left(3x^4-\dfrac{3}{4}x^3+2x^2-3\right)\)

`= 8x^4+1/5x^3-9x+2/5 - 3x^4+3/4x^3-2x^2+3`

`= (8x^4-3x^4)+(1/5x^3-3/4x^3)-2x^2-9x+(2/5+3)`

`= 5x^4 + 19/20x^3 -2x^2 -9x+17/5`

Answer 2

[Nguyễn Lê Phước Thịnh]

a: A(x)+B(x)=11x^4-11/20x^3+2x^2-9x-13/5

b: A(x)-B(x)=-5x^4-19/20x^3+2x^2+9x-17/5

c: B(x)-A(x)=5x^4+19/20x^3-2x^2-9x+17/5