Bài giải :
\(\frac{575757}{424242}\)= \(\frac{57}{45}\)
\(\frac{575757}{565656}\)= \(\frac{57}{56}\)
\(\frac{575757}{727272}\)= \(\frac{57}{72}\)
\(=>\) ( \(\frac{57}{45}\)+ \(\frac{57}{56}\)\(\frac{57}{72}\) ) x \(18\)\(=\)\(57\)
Hk tốt
\(A=\left(\frac{575757}{424242}+\frac{575757}{565656}+\frac{575757}{727272}\right)\times18\)
\(=\left(\frac{57\times10101}{42\times10101}+\frac{57\times10101}{56\times10101}+\frac{57\times10101}{72\times10101}\right)\times18\)
\(=\left(\frac{57}{42}+\frac{57}{56}+\frac{57}{72}\right)\times18\)
\(=57\left(\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\right)\times18\)
\(=\frac{57}{18}\times18=57\)
