tính nhanh 1/2+1/3+1/4+1/5+1/6-1/5-1/4-1/3-1/2
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\(\frac{1}{1}\times\frac{1}{2}+\frac{1}{2}\times\frac{1}{3}+\frac{1}{3}\times\frac{1}{4}+\frac{1}{4}\times\frac{1}{5}+\frac{1}{5}\times\frac{1}{6}=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}\)
\(=\frac{30}{60}+\frac{10}{60}+\frac{5}{60}+\frac{3}{60}+\frac{2}{60}\)
\(=\frac{50}{60}=\frac{5}{6}\)
Đáp án là 5/6 tick nha bạn
= \(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}\)
= \(1-\frac{1}{6}=\frac{5}{6}\)
\(\dfrac{2}{5}+\dfrac{1}{4}=\dfrac{8}{20}+\dfrac{5}{20}=\dfrac{13}{20}\)
\(\dfrac{1}{3}+\dfrac{3}{5}=\dfrac{5}{15}+\dfrac{9}{15}=\dfrac{14}{15}\)
\(\dfrac{1}{2}+\dfrac{1}{4}=\dfrac{2}{4}+\dfrac{1}{4}=\dfrac{3}{4}\)
\(\dfrac{1}{8}+\dfrac{5}{6}=\dfrac{3}{24}+\dfrac{20}{24}=\dfrac{23}{24}\)
(1/2+1/3+1/4+1/5+1/6+1/7)−(1/3+1/4+1/5+1/6+1/7+1/8)
= (1/2+1/8 )+(1/4+1/6 )+(1/6+1/4)−(1/3+1/7 )-(1/5 + 1/5 )
= 1/10 +1/10 +1/10 +1/10 -1/10
= 4/10 = 2/5
k mk na <3
1/2 + ( 1/3 - 1/3 ) + ( 1/4 - 1/4 ) + ( 1/5 -1/5 ) + ( 1/6 - 1/6 ) + ( 1/7 - 1/7 ) + 1/8
= 1/2 + 0 + 1/8
= 5/8
\(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{1}{6}-\frac{1}{5}-\frac{1}{4}-\frac{1}{3}-\frac{1}{2}\)
\(=\left(\frac{1}{2}-\frac{1}{2}\right)+\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{1}{4}-\frac{1}{4}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)+\frac{1}{6}\)
\(=0+0+0+0+\frac{1}{6}\)
\(=\frac{1}{6}\)
_Chúc bạn học tốt_
\(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{1}{6}-\frac{1}{5}-\frac{1}{4}-\frac{1}{3}-\frac{1}{2}\)
\(=\left(\frac{1}{2}-\frac{1}{2}\right)+\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{1}{4}-\frac{1}{4}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)+\frac{1}{6}\)
\(=0+0+0+0+\frac{1}{6}\)
\(=\frac{1}{6}\)