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1-2+3-4+5-6+................- 18+19
giai ra giup minh
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NK
17 tháng 4 2023
\(1-\dfrac{1}{2}=\dfrac{2}{2}-\dfrac{1}{2}=\dfrac{1}{2}\)
\(\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{3}{6}-\dfrac{2}{6}=\dfrac{1}{6}\)
\(\dfrac{1}{3}-\dfrac{1}{4}=\dfrac{4}{12}-\dfrac{3}{12}=\dfrac{1}{12}\)
\(\dfrac{1}{4}-\dfrac{1}{5}=\dfrac{5}{20}-\dfrac{4}{20}=\dfrac{1}{20}\)
\(\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{6}{30}-\dfrac{5}{30}=\dfrac{1}{30}\)
\(\dfrac{1}{6}-\dfrac{1}{7}=\dfrac{7}{42}-\dfrac{6}{42}=\dfrac{1}{42}\)
`@mt`
5 tháng 7 2023
1: =1/8*9/4=9/32
2: =8/27*243/32=9/4
3: =(5/4*4/5)^5*(4/5)^2=16/25
4: \(=\left(-\dfrac{5}{6}\cdot\dfrac{6}{5}\right)^2\cdot\left(\dfrac{6}{5}\right)^2=\dfrac{36}{25}\)
5: \(=\left(-\dfrac{4}{3}\right)^3\cdot\left(\dfrac{3}{4}\right)^{10}=\left(-1\right)\left(\dfrac{3}{4}\right)^7=-\left(\dfrac{3}{4}\right)^7\)
6: \(=\left(\dfrac{1}{3}\cdot\dfrac{-9}{2}\right)^4\left(-\dfrac{9}{2}\right)^2=\left(-\dfrac{3}{2}\right)^4\cdot\dfrac{81}{4}=\dfrac{9}{4}\cdot\dfrac{81}{4}=\dfrac{729}{16}\)
8: =(0,2*5)^4*5^2=25
10: =-0,5^5*2^10
=-0,5^5*2^5*2^5
=-32
13: =(0,5*2)^2*2^2=4
35:7
20 tháng 7 2023
1)1/6 - - 5/6 = 1/6 + 5/6 = 1
2)6/13 - -14/39 = 6/13 + 14/39= 32/39
3)4/5 - 4/-18 = 4/5 + 4/18= 46/45
4)7/21 - 9/-36 = 7/21 + 9/36 = 7/12
5)-12/18 - -21/35 = -12/18 + 21/35 = -1/15
6)-3/21 - 6/42 = -2/7
7)-18/24 - 15/21 = -41/28
8)1/6 - 2/5 =-7/30
Q
19 tháng 7 2017
a) \(142\cdot4^2-\left(7\cdot5^2+4x\right)=\left(4^3\cdot157\right):4^2\)
\(\Leftrightarrow142\cdot16-\left(7\cdot25+4x\right)=\left(64\cdot157\right):16\)
\(\Leftrightarrow2272-\left(175+4x\right)=10048:16\)
\(\Leftrightarrow2272-145-4x=628\)
\(\Leftrightarrow2097-4x=628\)
\(\Leftrightarrow-4x=-1469\)
\(\Leftrightarrow x=\dfrac{1469}{4}\)
Vậy \(x=\dfrac{1469}{4}\)
b) \(\left[\left(7x+23\right):6^2-5^2\right]:29=18^2\)
\(\Leftrightarrow\left(\dfrac{7x+23}{6^2}-25\right)\cdot\dfrac{1}{29}=18\)
\(\Leftrightarrow\left(\dfrac{7x+23}{36}-25\right)\cdot\dfrac{1}{29}=18\)
\(\Leftrightarrow\dfrac{7x+23-900}{36}\cdot\dfrac{1}{29}=18\)
\(\Leftrightarrow\dfrac{7x-877}{36}\cdot\dfrac{1}{29}=18\)
\(\Leftrightarrow\dfrac{7x-877}{1044}=18\)
\(\Leftrightarrow7x-877=18792\)
\(\Leftrightarrow7x=18792+877\)
\(\Leftrightarrow7x=19669\)
\(\Leftrightarrow x=\dfrac{19669}{7}\)
=10 nha bn
** mk nha
1-2+3-4+5-6+...+17-18+19
=(-1)+(-1)+(-1)+...+(-1)+19
=(-1).9+19
=-9+19
=10