tính = cách thuận tiện a) (1+1/2)+(1+1/3)+(1+1/4)+(1+1/5)+(1+1/6) B)(1-1/2)+(1-1/3)+(1-1/4)+(1-1/5)+(1-1/6)

Đáp án+Giải thích các bước giải:

$a) (1+\frac{1}{2})+(1+\frac{1}{3})+(1+\frac{1}{4})+(1+\frac{1}{5})+(1+\frac{1}{6})$

$=1\frac{1}{2}+1\frac{1}{3}+1\frac{1}{4}+1\frac{1}{5}+1\frac{1}{6}$

$=1\frac{360}{720}+1\frac{240}{720}+1\frac{180}{720}  +1\frac{144}{720}+1\frac{120}{720}$

$=1\frac{90}{1  80}+1\frac{60}{180}+1\frac{45}{180}+1\frac{36}{180}+1\frac{30}{180}$

$=\frac{270}{180}+\frac{240}{180}+\frac{225}{180}+\frac{216}{180}+\frac{210}{180}$

$=\frac{1160}{180}$

$b) (1-\frac{1}{2})+(1-\frac{1}{3})+(1-\frac{1}{4})+(1+-\frac{1}{5})+(1-\frac{1}{6})$

$=\frac{1}{2}+\frac{2}{3}+\frac{3}{4}+\frac{4}{5}+\frac{5}{6}$

$\frac{1}{2}+\frac{2}{3}+\frac{3}{4}+\frac{4}{5}+\frac{5}{6} $

$= \frac{1}{2}+\frac{2}{2}+\frac{3}{3}+\frac{4}{4}+\frac{5}{5}+\frac{6}{6} - \frac{1}{3} - \frac{1}{4} - \frac{1}{5} - \frac{1}{6}$

$= \frac{1}{2} + 1 + 1 + 1 + 1 - \frac{1}{3} - \frac{1}{4} - \frac{1}{5} - \frac{1}{6}$

$= \frac{1}{2} + \frac{12}{12} + \frac{20}{20} + \frac{20}{20} + \frac{20}{20} - \frac{10}{30} - \frac{7}{28} - \frac{6}{30} - \frac{5}{30}$

$= \frac{1+12+20+20+20-10-7-6-5}{30}$

$= \frac{63}{30}=\frac{21}{10}$

cho anh tlhn nha

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