Question

Tính tỉ số \(\frac{A}{B}\) biết :  A = \(\frac{4}{7\cdot31}\)+\(\frac{6}{7\cdot41}\)+\(\frac{9}{10\cdot41}\)+\(\frac{7}{10\cdot57}\)và  B = \(\frac{7}{19\cdot31}\)+ \(\frac{5}{19\cdot43}\) + \(\frac{3}{23\cdot43}\)+ \(\frac{11}{23\cdot57}\)

Answer 1

A=4/1.31+6/7.41+9/9.41+ 7/10.57

=20/35.31+30/35.41+45/45.41+35/50.57

=5(4/35.31+6/35.41+9/45.41+7/50.57)

=5(1/31-1/35+1/35-1/41+1/41-1/45+1/45-1/50+1/50-1/57)

=5(1/31-1/57)

B thì làm tương tự nhưng nhân với 2=> B=2(1/31-1/57)

=> A/B=5/2

Answer 2

A/B=5/2

Answer 3

Ai tk mình, mình  k lại

Answer 4

Cảm ơn nhưng mình cần lời giải đầy đủ bạn ạ.

Answer 5

Xét A

Ta có : A = \(\frac{1}{5}\)x \(\frac{4}{31\cdot35}\)+ \(\frac{1}{5}\)x \(\frac{6}{35\cdot41}\)+ \(\frac{1}{5}\)x \(\frac{9}{41\cdot50}\)+ \(\frac{1}{5}\)x \(\frac{7}{50\cdot57}\)

A = \(\frac{1}{5}\)x (\(\frac{4}{31\cdot35}\)+ \(\frac{6}{35\cdot41}\)+ \(\frac{9}{41\cdot50}\)+ \(\frac{7}{50\cdot57}\))

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

A = 1/5 x ( 1/31 - 1/57 )

Xét B

Ta có B = ...

( nhân với 1/2 rồi bạn tự làm nha )

( Good luck )

Answer 6

\(\frac{1}{5}A=\frac{4}{31.35}+....+\frac{7}{50.57}\)

\(\frac{1}{5}A=\frac{1}{31}-\frac{1}{35}+...+\frac{1}{50}-\frac{1}{57}\)

\(\frac{1}{5}A=\frac{1}{31}-\frac{1}{57}=\frac{26}{1767}\)

\(A=\frac{26}{\frac{1767}{\frac{1}{5}}}=\frac{130}{1767}\)

\(\frac{1}{2}B=\frac{7}{31.38}+....+\frac{11}{46.57}\)

\(\frac{1}{2}B=\frac{1}{31}-\frac{1}{38}+..+\frac{1}{46}-\frac{1}{57}\)

\(\frac{1}{2}B=\frac{1}{31}-\frac{1}{57}=\frac{26}{1767}\)

\(B=\frac{\frac{26}{1767}}{\frac{1}{2}}=\frac{52}{1767}\)

\(\frac{A}{B}=\frac{130}{\frac{1767}{\frac{52}{1767}}}=\frac{5}{2}\)