Question

1 .Thực hiện phép tính :

\(8x^{n-1}.\left(\dfrac{1}{2}.x^{n+1}-\dfrac{3}{4}.x\right)\)

2. Tìm x , biết :

a, \(3x.\left(2x-4\right)-2x\left(2x+5\right)=44\)

b, \(x.\left(5-3x\right)+3x.\left(x+1\right)=40\)

Answer 1

1/ \(8x^{n-1}\left(\dfrac{1}{2}x^{n+1}-\dfrac{3}{4}x\right)=4x^{2n}-6x^n\)

2/

a/ \(3x\left(2x-4\right)-2x\left(2x+5\right)=44\)

\(\Leftrightarrow6x^2-12x-4x^2-10x=44\)

\(\Leftrightarrow2x^2-22x=44\)

\(\Leftrightarrow2x^2-22x-44=0\)

\(\Leftrightarrow\left\{{}\begin{matrix}x_1=\dfrac{11+\sqrt{209}}{2}\\x_2=\dfrac{11-\sqrt{209}}{2}\end{matrix}\right.\)

b/ \(x\left(5-3x\right)+3x\left(x+1\right)=40\)

\(\Leftrightarrow5x-3x^2+3x^2+3x=40\)

\(\Leftrightarrow8x=40\)

\(\Leftrightarrow x=5\)

Vậy....................