`987`\(\times34+65\times987+978+9\)

\(=987\times\left(34+65\right)+978+9\)

\(=987\times99+978+9\)

\(=97713+978+9\)

\(=98691+9=98700\)

Hbth cop AI => ghi TK ah!

\(Ư\left(15\right)=\left\{1;3;5;15\right\}\)

Mở rộng : \(Ư\left(15\right)=\left\{\pm1;\pm3;\pm5;\pm15\right\}\)

\(81:3^2+5\times4^2-7\times3^2\)

\(=81:9-5\times16-7\times9\)

\(=9-80-63\)

\(=-71-63=-134\)

\(x^2=144\)

\(\Rightarrow x^2=\left(\pm12\right)^2\)

\(\Rightarrow x\in\left\{\pm12\right\}\)

\(a=23\times23=529\)

$\Rightarrow$\(x=123\times4+529\)

\(\Rightarrow x=492+529=1021\)

off lâu quá , mình thành ng tối cổ rùi :>>

$(\frac{2}{7} + \frac {4}{9}) + \frac {5}{7}$

$= \frac {2}{7} + \frac {4}{9} + \frac {5}{7}$

$= (\frac{2}{7} + \frac{5}{7}) + \frac{4}{9}$

$=  1 + \frac{4}{9} = \frac{13}{9}$

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