Tính hợp lý: 1)-5/14+3/8-2/14-3/8+1/2 2)7/15-5/7-(3/5-23/15-5/7) 3)11/15×12/13-7/30+11/15×14/13 4)5/7(1/2-1/3+4/7)+(1/3-1/2-

1 bình luận về “Tính hợp lý: 1)-5/14+3/8-2/14-3/8+1/2 2)7/15-5/7-(3/5-23/15-5/7) 3)11/15×12/13-7/30+11/15×14/13 4)5/7(1/2-1/3+4/7)+(1/3-1/2-”

1. 1) $\frac{-5}{14}$ + $\frac{3}{8}$ – $\frac{2}{14}$ – $\frac{3}{8}$ +$\frac{1}{2}$  

   = ($\frac{3}{8}$ – $\frac{3}{8}$) + ($\frac{-5}{14}$ – $\frac{2}{14}$) + $\frac{1}{2}$ 

   = $\frac{-1}{2}$ + $\frac{-1}{2}$

   =0.

   2) $\frac{7}{15}$ – $\frac{5}{7}$ – ($\frac{3}{5}$ – $\frac{23}{15}$ – $\frac{5}{7}$) 

   = $\frac{7}{15}$ – $\frac{5}{7}$ – $\frac{3}{5}$ + $\frac{23}{15}$ + $\frac{5}{7}$ 

   = (-$\frac{5}{7}$ +  $\frac{5}{7}$) + ($\frac{7}{15}$ + $\frac{23}{15}$) – $\frac{3}{5}$ 

   = $\frac{30}{15}$ – $\frac{3}{5}$ 

   = $\frac{10}{5}$ – $\frac{3}{5}$ 

   = $\frac{7}{5}$ 

   3) $\frac{11}{15}$ . $\frac{12}{13}$ – $\frac{7}{30}$ + $\frac{11}{15}$ . $\frac{14}{13}$

   = $\frac{11}{15}$ . ($\frac{12}{13}$ + $\frac{14}{13}$) –  $\frac{7}{30}$ 

   = $\frac{11}{15}$ . 2 – $\frac{7}{30}$ 

   = $\frac{22}{30}$ – $\frac{7}{30}$ 

   = $\frac{15}{30}$ = $\frac{1}{2}$

   4) $\frac{5}{7}$.($\frac{1}{2}$-$\frac{1}{3}$+$\frac{4}{7}$)+($\frac{1}{3}$-$\frac{1}{2}$-$\frac{4}{7}$) : $\frac{7}{5}$  

   = $\frac{5}{7}$.($\frac{1}{2}$-$\frac{1}{3}$+$\frac{4}{7}$)+($\frac{1}{3}$-$\frac{1}{2}$-$\frac{4}{7}$). $\frac{5}{7}$

   = $\frac{5}{7}$. ($\frac{1}{2}$-$\frac{1}{3}$+$\frac{4}{7}$+$\frac{1}{3}$-$\frac{1}{2}$-$\frac{4}{7}$)

   = $\frac{5}{7}$. [($\frac{1}{2}$-$\frac{1}{2}$)+(-$\frac{1}{3}$+$\frac{1}{3}$)+($\frac{4}{7}$-$\frac{4}{7}$)]

   = $\frac{5}{7}$. 0

   = 0

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