tính bang cách nhanh nhất
3+8-1+6-7+9-2+4=
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\(=\dfrac{3}{7}\cdot\left(\dfrac{4}{9}+\dfrac{5}{9}+1\right)=\dfrac{3}{7}\cdot2=\dfrac{6}{7}\)
\(=\dfrac{3}{7}\times\dfrac{4}{9}\times\dfrac{5}{9}\times\dfrac{3}{7}+\dfrac{3}{7}=\dfrac{3}{7}\times\left(\dfrac{4}{9}+\dfrac{5}{9}+1\right)=\dfrac{3}{7}\times2=\dfrac{6}{7}\)
1/2 + 2/3 - 3/4 * 4/5 * 5/6 * 6/7 * 7/8 * 8/9 *...* 29/30 : 6/10
= 1/2 + 2/3 - 1/10 : 6/10
= 1/2 + 2/3 - 1/6
= 1
`3+1/9+3/9+2+5/9+3+2`
`= ( 3 +2+3+2) +(1/9+ 3/9 + 5/9)`
`= 10 + 9/9`
`=10 + 1`
`=11`
\(3+\dfrac{1}{9}+\dfrac{3}{9}+2+\dfrac{5}{9}+3+2\)
\(=3+\left(\dfrac{1}{9}+\dfrac{3}{9}+\dfrac{5}{9}\right)+2+3+2\)
\(=\left(3+2+3+2\right)+\dfrac{9}{9}\)
\(=10+1=11\)
\(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}\\ =\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)\\ =\dfrac{5}{5}+\dfrac{22}{11}+\dfrac{26}{13}\\ =1+2+2\\ =5\)
=20 nha
20 nha bạn