tính nhanh 1/2+5/14 +2/63 +3/108 +1/156 08/09/2021 Bởi Peyton tính nhanh 1/2+5/14 +2/63 +3/108 +1/156
Ta có $\dfrac{1}{2} + \dfrac{5}{2.7} + \dfrac{2}{7.9} + \dfrac{3}{12.9} + \dfrac{1}{156}$ $= \dfrac{7}{14} + \dfrac{5}{14} + \dfrac{24}{7.12.9} + \dfrac{21}{7.12.9} + \dfrac{1}{156}$ $= \dfrac{12}{14} + \dfrac{45}{7.12.9} + \dfrac{1}{156}$ $= \dfrac{6}{7} + \dfrac{5}{84} + \dfrac{1}{156}$ $= \dfrac{72}{84} + \dfrac{5}{84} + \dfrac{1}{156}$ $= \dfrac{77}{84} + \dfrac{1}{156}$ $= \dfrac{11}{12} + \dfrac{1}{12.13}$ $= \dfrac{11.13}{12.13} + \dfrac{1}{12.13}$ $= \dfrac{143 + 1}{12.13}$ $= \dfrac{12}{13}$ Vậy đáp án là $\dfrac{12}{13}$. Bình luận
Đáp án:12/13 nha
Ta có
$\dfrac{1}{2} + \dfrac{5}{2.7} + \dfrac{2}{7.9} + \dfrac{3}{12.9} + \dfrac{1}{156}$
$= \dfrac{7}{14} + \dfrac{5}{14} + \dfrac{24}{7.12.9} + \dfrac{21}{7.12.9} + \dfrac{1}{156}$
$= \dfrac{12}{14} + \dfrac{45}{7.12.9} + \dfrac{1}{156}$
$= \dfrac{6}{7} + \dfrac{5}{84} + \dfrac{1}{156}$
$= \dfrac{72}{84} + \dfrac{5}{84} + \dfrac{1}{156}$
$= \dfrac{77}{84} + \dfrac{1}{156}$
$= \dfrac{11}{12} + \dfrac{1}{12.13}$
$= \dfrac{11.13}{12.13} + \dfrac{1}{12.13}$
$= \dfrac{143 + 1}{12.13}$
$= \dfrac{12}{13}$
Vậy đáp án là $\dfrac{12}{13}$.