Cách 1 :
A = $\frac{2}{3}$ + $\frac{3}{4}$ - $\frac{4}{5}$
= $\frac{40}{60}$ + $\frac{45}{60}$ - $\frac{48}{60}$
= $\frac{85}{60}$ - $\frac{48}{60}$
= $\frac{37}{60}$
B = $\frac{5}{6}$ - $\frac{7}{8}$ + $\frac{9}{10}$
= $\frac{100}{120}$ - $\frac{105}{120}$ + $\frac{108}{120}$
= $\frac{-5}{120}$ + $\frac{108}{120}$
= $\frac{103}{120}$
C = $\frac{1}{2}$ + $\frac{1}{8}$ - $\frac{1}{10}$
= $\frac{20}{40}$ + $\frac{5}{40}$ - $\frac{4}{40}$
= $\frac{25}{40}$ - $\frac{4}{40}$
= $\frac{21}{40}$
Ta có : A + B + C
= $\frac{37}{60}$ + $\frac{103}{120}$ + $\frac{21}{40}$
= $\frac{74}{120}$ + $\frac{103}{120}$ + $\frac{63}{120}$
= $\frac{177}{120}$ + $\frac{63}{120}$
= $\frac{240}{120}$
= 2
Cách 2 :
Ta có : A + B + C
= $\frac{2}{3}$ + $\frac{3}{4}$ - $\frac{4}{5}$ +$\frac{5}{6}$ - $\frac{7}{8}$ + $\frac{9}{10}$ + $\frac{1}{2}$ + $\frac{1}{8}$ - $\frac{1}{10}$
= $\frac{2}{3}$ + $\frac{5}{6}$ + $\frac{3}{4}$ + $\frac{1}{2}$ - $\frac{7}{8}$ + $\frac{1}{8}$ + $\frac{9}{10}$ - $\frac{1}{10}$ - $\frac{4}{5}$
= $\frac{9}{6}$ + $\frac{5}{4}$ - $\frac{6}{8}$ + $\frac{8}{10}$ - $\frac{4}{5}$
= $\frac{3}{2}$ + $\frac{5}{4}$ - $\frac{3}{4}$ + $\frac{4}{5}$ - $\frac{4}{5}$
= $\frac{3}{2}$ + $\frac{1}{2}$
= $\frac{4}{2}$
= 2
~CHÚC BẠN HỌC TỐT~
