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a) 1 - 5 + 9 - 13 + .... + 393 - 397
= ( 1 - 5 ) + ( 9 - 13 ) + ... + ( 393 - 397 )
= ( -4 ) + ( -4 ) + ... + ( -4 )
= ( -4 ) x 197
= -788
b) - 2 + 4 - 6 + 8 - ... - 238 + 240
= ( -2 + 4 ) + ( -6 + 8 ) + ... + ( -238 + 240 )
= 2 + 2 + ... + 2
= 2 x 60
= 140
`8 2/7-(3 4/9+4 2/7)`
`=8+2/7-(3+4/9+4+2/7)`
`=8+2/7-7-2/7-4/9`
`=1-4/9`
`=5/9`
8 2/7-(3 4/9+4 2/7)
=58/7-31/9-30/7
=(58/7-30/7)-31/9
=4-31/9
=5/9
a) (-124) + 24 = -100
b) 37. 78 + 37. 22
= 37 . ( 78 + 22 )
= 37 . 100
= 3700
1) = (8/31 + 23/31)+ ( -12/25+-13/25) = 1 + (-1) = 0
2) = 1/2 +3/4 -3/4 + 4/5 = 1/2 +4/5 = 13/10
3)= ( 7/3 x 15/21) x ( -5/2 x 4/-5 ) = ( 7/3 x 5/7 ) x 2 = 5/3 x 2 = 10/3
4) = 1/4 + 3/4 x -7/6 = 1/4 + -7/8 = -5/8
5)= 3/29 x 29/3 - 1/5 x 29/3 = 1 x 29/15 = 29/15
6)= 5/7 x ( 5/11 + 2/11 - 14/11) = 5/7 x -7/11 = -5 /11
7) = 11/12 x -1/8 + 11/12 x -3/16 - 11/12 = 11/12 x ( -1/8 + -3/16 - 1) = 11/12 x -21/16 = -77/64 ( mk ko chắc , bạn ấn máy tính để thử lại )
8) = 203/20 - 7/4 + 41/13 = 198/20 + 41/13 = 99/10 + 41/13 = 1697/130 ( câu này cứ lỏ lỏ kiểu gì ý :v )
1) = (8/31 + 23/31)+ ( -12/25+-13/25) = 1 + (-1) = 0
2) = 1/2 +3/4 -3/4 + 4/5 = 1/2 +4/5 = 13/10
3)= ( 7/3 x 15/21) x ( -5/2 x 4/-5 ) = ( 7/3 x 5/7 ) x 2 = 5/3 x 2 = 10/3
4) = 1/4 + 3/4 x -7/6 = 1/4 + -7/8 = -5/8
5)= 3/29 x 29/3 - 1/5 x 29/3 = 1 x 29/15 = 29/15
6)= 5/7 x ( 5/11 + 2/11 - 14/11) = 5/7 x -7/11 = -5 /11
7) = 11/12 x -1/8 + 11/12 x -3/16 - 11/12 = 11/12 x ( -1/8 + -3/16 - 1) = 11/12 x -21/16 = -77/64 ( mk ko chắc , bạn ấn máy tính để thử lại )
8) = 203/20 - 7/4 + 41/13 = 198/20 + 41/13 = 99/10 + 41/13 = 1697/130 ( câu này cứ lỏ lỏ kiểu gì ý :v )
\(=\dfrac{-3}{4}-\dfrac{1}{2}-\dfrac{3}{4}+\dfrac{5}{8}=\dfrac{-6}{4}+\dfrac{5}{8}-\dfrac{1}{2}=-2+\dfrac{5}{8}=\dfrac{-16+5}{8}=-\dfrac{11}{8}\)
Bài 2:
Ta thấy: 52 > 4.5
62 > 5.6
72 > 6.7
....
20172 > 2016.2017
\(\Rightarrow\)\(\frac{1}{5^2}< \frac{1}{4.5}\)
\(\frac{1}{6^2}< \frac{1}{5.6}\)
\(\frac{1}{7^2}< \frac{1}{6.7}\)
....
\(\frac{1}{2017^2}< \frac{1}{2016.2017}\)
Cộng vế với nhau, ta có:
\(\frac{1}{5^2}+\frac{1}{6^2}+\frac{1}{7^2}+...+\frac{1}{2017^2}\) < \(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{2016.2017}\)
\(\Rightarrow\)A < \(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{2016}-\frac{1}{2017}\)
\(\Rightarrow\)A < \(\frac{1}{4}-\frac{1}{2017}\)
\(\Rightarrow\)A < \(\frac{1}{4}\)( vì \(\frac{1}{2017}>0\))
k giúp mik ✅
e: =5/7(5/11+2/11-14/11)
=5/7(-7/11)=-5/11
f: =-5/4(2/11+9/11)+1+3/4
=-5/4+7/4
=2/4=1/2
g: =-5/7(3/13+10/13)+1+5/7
=-5/7+1+5/7
=1
h: =7/4(29/5-9/5)+41/13
=-7+41/13=-50/13
\(a)\)
\(\left(-31\right)+\left(50-19\right)-\left(150-31\right)\)
\(=\left(-31\right)+50-19-150+31\)
\(=\left(-150\right)-19\)
\(=-169\)
\(b)\)
\(25.\left(45-17\right)-45.\left(25-17\right)\)
\(=25.45-25.17-45.25+45.17\)
\(=0\)
\(c)\)
\(\frac{-1}{12}+\frac{4}{3}=\frac{5}{4}\)
\(d)\)
\(3+\frac{-5}{20}+\frac{30}{75}+\frac{-7}{4}\)
\(=\left(\frac{3}{5}+\frac{30}{75}\right)-\left(\frac{5}{20}+\frac{7}{4}\right)\)
\(=1-2\)
\(=-1\)
a) (-31)+(50-19)-(150-31)
= (-31)+50+(-19)-150+(-31)
= (-31)+50-150+(-19)-(-31)
= (-31)+(-100)+12
= -119
b) 25(45-17)-45(25-17)
= 25.45-25.17-45.25-45.17
= 25(45-45)-25(17-17)
= 0
c) -1/12 + 4/3
= -1/12 + 16/12
= 15/12
= 5/4
d) 3/5+(-5)/20+30/75+(-7)/4
= 45/75+30/75+(-5)/20+(-35)/20
= 1+(-2)
= -1
`2-3 3/4:(5/8-20%)`
`=2-3 3/4:(5/8-1/4)`
`=2-15/4:3/8`
`=2-10`
`=-8`
\(2-3\dfrac{3}{4}:\left(\dfrac{5}{8}-20\%\right)\)
\(=2-\dfrac{15}{4}:\left(\dfrac{5}{8}-\dfrac{20}{100}\right)\)
\(=\dfrac{2}{1}-\dfrac{15}{4}:\left(\dfrac{5}{8}-\dfrac{1}{5}\right)\)
\(=\dfrac{2}{1}-\dfrac{15}{4}:\left(\dfrac{25}{40}-\dfrac{8}{40}\right)\)
\(=\dfrac{2}{1}-\dfrac{15}{4}:\dfrac{17}{40}\)
\(=\dfrac{2}{1}-\dfrac{15}{4}.\dfrac{40}{17}\)
\(=\dfrac{2}{1}-\dfrac{600}{68}\)
\(=\dfrac{2}{1}-\dfrac{150}{17}\)
\(=\dfrac{34}{17}-\dfrac{150}{17}\)
\(=\dfrac{-116}{17}\)