Tính bằng cách thuận tiện nhất
1 3 × 4 3 + 4 3 × 5 3 + 4 3 + 2 =
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\(\dfrac{1}{4}+\dfrac{2}{5}+\dfrac{3}{4}+\dfrac{3}{5}\)
\(=\left(\dfrac{1}{4}+\dfrac{3}{4}\right)+\left(\dfrac{2}{5}+\dfrac{3}{5}\right)\)
\(=1+1\)
\(=2\)
#Sahara |
\(\frac{3}{1\times2}+\frac{3}{2\times3}+...+\frac{3}{5\times6}\)
\(=3\left(\frac{1}{1\times2}+\frac{1}{2\times3}+...+\frac{1}{5\times6}\right)\)
\(=3\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{5}-\frac{1}{6}\right)\)
\(=3\left(1-\frac{1}{6}\right)=3\times\frac{5}{6}=\frac{5}{2}\)
\(\frac{3}{4}+\frac{2}{5}+\frac{1}{4}+\frac{3}{5}\)
\(\Leftrightarrow\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)\)
\(=1+1\)
\(=2\)
\(\frac{3}{4}+\frac{2}{5}+\frac{1}{4}+\frac{3}{5}.\)
\(=\left(\frac{3}{4}+\frac{1}{4}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)\)
\(=\frac{4}{4}+\frac{5}{5}\)
\(=1+1\)
\(=2\)
5,5 + \(\dfrac{3}{4}\) - 5 + \(\dfrac{1}{4}\)
(5,5 - 5) + (\(\dfrac{3}{4}\) + \(\dfrac{1}{4}\))
= 0,5 + 1
= 1,5
\(\dfrac{5}{2}\) x \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) : \(\dfrac{3}{2}\)
= \(\dfrac{5}{2}\) x \(\dfrac{2}{3}\) + \(\dfrac{1}{4}\) x \(\dfrac{2}{3}\)
= (\(\dfrac{5}{2}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)
= (\(\dfrac{10}{4}\) + \(\dfrac{1}{4}\)) x \(\dfrac{2}{3}\)
= \(\dfrac{11}{4}\) x \(\dfrac{2}{3}\)
= \(\dfrac{11}{6}\)
Tính \(x\):
435 - [\(x\) + 16] = 425 : 17
435 - [\(x\) + 16] = 25
[\(x\) + 16] = 435 - 25
\(x\) + 16 = 410
\(x\) = 410 - 16
\(x\) = 394
= 3/2 + 2/3 + 2/4 + 2/5
= (6/4 + 2/4) + (2/3 + 2/5)
= 8/4 + 16/ 15
= 46/15
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#Hok_tốt
3/1*2 + 3/2*3 + 3/3*4 + 3/4*5 + 3/5*6
= 3 * ( 1/1*2 + 1/2*3 + 1/3*4 + 1/4*5 + 1/5*6 )
= 3 * (1/1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/5 - 1/5 - 1/6)
= 3 * (1/1 - 1/6)
= 3 * 5/6
= 5/2
HOK TỐT