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

\(\Leftrightarrow\left(x-1\right)^2-4\left(x-1\right)=0\)

\(\Leftrightarrow\left(x-1-4\right)\left(x-1\right)=0\Leftrightarrow x=5;1\)

\(\frac{20x^2-45}{\left(2x+3\right)^2}=\frac{5\left(4x^2-9\right)}{\left(2x+3\right)^2}=\frac{5\left(2x-3\right)\left(2x+3\right)}{\left(2x+3\right)^2}=\frac{5\left(2x-3\right)}{2x+3}\)( ĐKXĐ : x ≠ -3/2 )

\(\frac{5x^2-10xy}{2\left(2y-x\right)^3}=\frac{-\left(10xy-5x^2\right)}{2\left(2y-x\right)^3}=\frac{-5x\left(2y-x\right)}{2\left(2y-x\right)^3}=\frac{-5x}{2\left(2y-x\right)^2}\)( ĐKXĐ : y ≠ x/2 )

\(\frac{80x^3-125x}{3\left(x-3\right)-\left(x-3\right)\left(8-4x\right)}=\frac{5x\left(16x^2-25\right)}{\left(x-3\right)\left(3-8+4x\right)}=\frac{5x\left(4x-5\right)\left(4x+5\right)}{\left(x-3\right)\left(4x-5\right)}=\frac{5x\left(4x+5\right)}{x-3}\)

( ĐKXĐ : x ≠ 3 ; x ≠ 5/4 )

Xét tứ giác ABCD có:

                                A+B+C+D=360

                           <=> 130+70+110+D=360

                            <=> D= 360-(130+70+110)=50

Vậy góc D bằng 50 độ.

Vì tứ giác ABCD có tổng số đo là 360^0 

=)) ^A + ^B + ^C + ^D = 360^0

<=> ^D = 360^0 - ^A - ^B - ^C 

<=> ^D = 360^0 - 130^0 - 70^0 - 110^0

<=> ^D = 80^0 

Vật ^D = 80^0 

\(\frac{2a}{b^2}\)( ĐKXĐ : b ≠ 0 )

\(\frac{x}{2a+2b}=\frac{x}{2\left(a+b\right)}\)( ĐKXĐ : a ≠ -b )

\(\frac{y}{a^2-b^2}=\frac{y}{\left(a-b\right)\left(a+b\right)}\)( ĐKXĐ : a ≠ ±b )

MTC : \(2b^2\left(a-b\right)\left(a+b\right)\)

\(\frac{x}{4+2a}=\frac{x}{2a+4}=\frac{x}{2\left(a+2\right)}\)( ĐKXĐ : a ≠ -2 )

\(\frac{y}{4-2a}=\frac{-y}{2a-4}=\frac{-y}{2\left(a-2\right)}\)( ĐKXĐ : a ≠ 2 )

\(\frac{z}{4-a^2}=\frac{-z}{a^2-4}=\frac{-z}{\left(a-2\right)\left(a+2\right)}\)( ĐKXĐ : a ≠ ±2 )

MTC : \(2\left(a-2\right)\left(a+2\right)\)

\(\frac{5}{2x-4}=\frac{5}{2\left(x-2\right)}\)( ĐKXĐ : x ≠ 2 )

\(\frac{4}{3x-9}=\frac{4}{3\left(x-3\right)}\)( ĐKXĐ : x ≠ 3 )

\(\frac{7}{50-25x}=\frac{-7}{25x-50}=\frac{-7}{25\left(x-2\right)}\)( ĐKXĐ : x ≠ 2 )

MTC : \(150\left(x-2\right)\left(x-3\right)\)

đề bài?

Chứng minh rằng với mọi N thuộc Z Thì

A=n ^ 3 - 4n chia hết cho 3

B= 2n ^ 3- 6n ^2 + 16 chia hết cho 12