\(A=\dfrac{20}{35\cdot31}+\dfrac{30}{35\cdot41}+\dfrac{45}{41\cdot50}+\dfrac{35}{50\cdot57}\)

=5(4/31*35+6/35*41+9/41*50+7/50*57)

=5(1/31-1/35+1/35-1/41+1/41-1/50+1/50-1/57)

=5*(1/31-1/57)

=130/1767

Quyền đây

=>x*5/57=130/1767

=>x=26/31

Đặt A là tên của biểu thức

\(A=\frac{4}{7.31}+\frac{6}{7.41}+\frac{9}{10.41}+\frac{7}{10.57}\)

\(=\frac{20}{31.35}+\frac{30}{35.41}+\frac{45}{41.50}+\frac{35}{50.57}\)

\(=5\left(\frac{4}{31.35}+\frac{6}{35.41}+\frac{9}{41.50}+\frac{7}{50.57}\right)\)

\(=5\left(\frac{1}{31}-\frac{1}{35}+\frac{1}{35}-\frac{1}{41}+\frac{1}{41}-\frac{1}{50}+\frac{1}{50}-\frac{1}{57}\right)\)

\(=5\left(\frac{1}{31}-\frac{1}{57}\right)=5\cdot\frac{26}{1767}=\frac{130}{1767}\)

130/1767

\(B=\dfrac{14}{38\cdot31}+\dfrac{10}{38\cdot43}+\dfrac{6}{43\cdot46}+\dfrac{22}{46\cdot57}\)

=2(7/31*38+5/38*43+3/43*46+11/46*57)

=2(1/31-1/38+1/38-1/43+...+1/46-1/57)

=>A/B=5/2

5/2 nhé

\(\frac{5}{7}\times x=\frac{20}{35\times31}+\frac{30}{35\times41}+\frac{45}{50\times41}+\frac{35}{50\times57}\)

\(\frac{5}{7}\times x=5\times\left(\frac{4}{35\times31}+\frac{6}{35\times41}+\frac{9}{50\times41}+\frac{7}{50\times57}\right)\)

\(\frac{5}{7}\times x=5\times\left(\frac{1}{31}-\frac{1}{35}+\frac{1}{35}-\frac{1}{41}+\frac{1}{41}-\frac{1}{50}+\frac{1}{50}-\frac{1}{57}\right)\)

\(\frac{5}{7}\times x=5\times\left(\frac{1}{31}-\frac{1}{57}\right)\)

\(x=5\times\frac{26}{1767}:\frac{5}{7}\)

\(x=7\times\frac{26}{1767}\)

\(x=\frac{182}{1767}\)

Vậy \(x=\frac{182}{1767}\)

Nếu thấy đúng thì cho mình vài cái h đúng nha!!!