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1 nhé bạn

1

(số nào nhân với 1 bằng chính nó)

minh biet

ta có : 

\(\left|x+1\right|+\left|x-1\right|=1+\left|\left(x-1\right)\left(x+1\right)\right|\)

\(\Leftrightarrow\left|x-1\right|\left|x+1\right|-\left|x-1\right|-\left|x+1\right|+1=0\)

\(\Leftrightarrow\left(\left|x-1\right|-1\right)\left(\left|x+1\right|-1\right)=0\Leftrightarrow\orbr{\begin{cases}\left|x-1\right|=1\\\left|x+1\right|=1\end{cases}}\)

\(\Leftrightarrow x\in\left\{-2,0,2\right\}\)

Ta có: \(P=1\frac13\times1\frac18\times1\frac{1}{15}\times\ldots\times1\frac{1}{80}\times1\frac{1}{99}\)

\(=\frac43\times\frac98\times\frac{16}{15}\times\ldots\times\frac{81}{80}\times\frac{100}{99}\)

\(=\frac{2\times2}{1\times3}\times\frac{3\times3}{2\times4}\times\ldots\times\frac{10\times10}{9\times11}\)

\(=\frac{2\times3\times\ldots\times10}{1\times2\times\ldots\times9}\times\frac{2\times3\times\ldots\times10}{3\times4\times\ldots\times11}=\frac{10}{1}\times\frac{2}{11}=\frac{20}{11}\)

B=3/2x4/3x...........x2018/2017

=3x4x5x...........x2018/2x3x2x2x............x2017

=2x2018

=4036

A,C tương tự

a, \(=\dfrac{1.2.3...5}{2.3...6}=\dfrac{1}{6}\)