Question

BÀI 2: rút gọn biểu thức 

a) 2x( 5-3x^2) - 10( 6+x)

b)3(-x+2)-6( 1-x+5x^20)

c) 7x( 2-5x^2+1/2x^3)- 14x( 1-2x^2)

Answer 1

a)      \(2x\left(5-3x^2\right)-10\left(6+x\right)\)

     \(=10x-6x^3-60-10x\)

     \(=\) \(-6x^3-60\)

Answer 2

a) \(2x\left(5-3x^2\right)-10\left(6+x\right)\\ =2x.5-2x.3x^2-10.6-10.x\\ =10x-6x^3-60-10x\)

b) \(3\left(-x+2\right)-6\left(1-x+5x^{20}\right)\\ =-3.x+3.2-6.1+6.x-5.5x^{20}\\ =-3x+6-6+6x-25x^{20}=25x^{20}+3x\)

c) \(7x\left(2-5x^2+\dfrac{1}{2}x^3\right)-14x\left(1-2x^2\right)\\ =7x.2-7x.5x^2+7x.\dfrac{1}{2}x^3-14x.1+14x.2x^2\\ =14x-25x^3+\dfrac{7}{2}x^4-14x+28x^3=3x^2+\dfrac{7}{2}x^4\) 

Answer 3

b)    \(3\left(-x+2\right)-6\left(1-x+5x^{20}\right)\)

  \(=-3x+6-6+6x-30x^{20}\)

  \(=3x-30x^{20}\)

Answer 4

c)   \(7x\left(2-5x^2+\dfrac{1}{2}x^3\right)-14x\left(1-2x^2\right)\)

  \(=14x-35x^3+3,5x^4-14x+28x^3\)

  \(=-7x^3+3,5x^4\)

Answer 5

a) Ta có: \(2x\left(5-3x^2\right)-10\left(6+x\right)\)

\(=10x-6x^3-60-10x\)

\(=-6x^3-60\)

b) Ta có: \(-3\left(-x+2\right)-6\left(1-x+5x^{20}\right)\)

\(=3x-6-6+6x-30x^{20}\)

\(=-30x^{20}+9x-12\)

Answer 6

c) Ta có: \(7x\left(2-5x^2+\dfrac{1}{2}x^3\right)-14\left(1-2x^2\right)\)

\(=14-35x^3+\dfrac{7}{2}x^4-14+28x^2\)

\(=\dfrac{7}{2}x^4-35x^3+28x^2\)