Question

Tính nhanh:

a, \(\frac{7}{13}\) . \(\frac{7}{15}\)  - \(\frac{5}{12}\) . \(\frac{21}{39}\) + \(\frac{49}{91}\) . \(\frac{8}{15}\)

:"(( Ai làm giúp đii 

Answer 1

\(\frac{7}{13}.\frac{7}{15}-\frac{5}{12}.\frac{21}{39}+\frac{49}{91}.\frac{8}{15}\\ =\frac{7}{13}.\frac{7}{15}-\frac{5}{12}.\frac{7}{13}+\frac{7}{13}.\frac{8}{15}\\ =\frac{7}{13}\left(\frac{7}{15}-\frac{5}{12}+\frac{8}{15}\right)\\ =\frac{7}{13}\left(\frac{7}{15}+\frac{8}{15}-\frac{5}{12}\right)\\ =\frac{7}{13}\left(1-\frac{5}{12}\right)\\ =\frac{7}{13}.\frac{712}{ }\)

\(\frac{7}{13}.\frac{7}{12}=\frac{49}{156}\)