Question

1. rút gọn

a. x² (x + 2) - 3x (x² - 1)

b. x³ (x-4) + (x² + 3) (-x) - x⁴

2. tìm x , biết:

a. 2x (x - 5) - x (3 + 2x)= 26

b. x (x² + x + 1 ) - x² (x+ 1) - x + 5 = 4

Answer 1

B1:

a) \(x^2\left(x+2\right)-3x\left(x^2-1\right)\)

= \(x^3+2x^2-3x^3+3x=-2x^3+2x^2+3x\)

b) \(x^3\left(x-4\right)+\left(x^2+3\right)\left(-x\right)-x^4\)

= \(x^4-4x^3-x^3-3x-x^4=-5x^3-3x\)

B2:

a) \(2x\left(x-5\right)-x\left(3+2x\right)=26\)

\(2x^2-10x-3x-2x^2-26=0\)

\(-13x-26=0\)

\(-13\left(x+2\right)=0\)

\(\Rightarrow x+2=0\Rightarrow x=-2\)

b) \(x\left(x^2+x+1\right)-x^2\left(x+1\right)-x+5=4\)

\(x^3+x^2+x-x^2-x^3-x^2-x+5-4=0\)

\(-x^2+1=0\Rightarrow-x^2=-1\Rightarrow x=\pm1\)

Answer 2

\(x^2\left(x+2\right)-3x\left(x^2-1\right)\)

\(=x^3+2x^2-3x^3-3x\)

\(=-2x^3+2x^2-3x\)

\(x^3\left(x-4\right)+\left(x^2+3\right)\left(-x\right)-x^4\)

\(=x^4-4x^3+-x^3-3x-x^4\)

\(=-5x^3-3x\)