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a) 13.7 + 7.7
= (13 + 7).7
= 20 . 7
= 140
b) 23 . 2016 . 52
= 8 . 2016 . 25
= 200 . 2016
= 403200
c) 32 . 15 - 5.9
= 9.15 - 5.9
= (15 - 5).9
= 10.9
= 90
d) 13 + 15 + ........... + 57 + 59
Áp dụng công thức tính dãy số ta có :
\(\frac{\left[\left(59-13\right):2+1\right].\left(59+13\right)}{2}=\frac{24.72}{2}=864\)
a) 13 . 7 + 7 . 7
= (13 + 7) . 7
= 20 . 7
= 140
b) 23 . 2016 . 52
= 8 . 2016 . 25
= ( 8 . 25 ) . 2016
= 200 . 2016
= 403200
c) 32 . 15 - 5 . 9
= 9 . 15 - 45
= 9 . 15 - 15 . 3
= ( 9 - 3 ) . 15
= 6 . 15
= 90
d) 13 + 15 + ........ + 57 + 59
Dãy số trên có số số hạng là:
( 59 - 13 ) : 2 + 1= 24 ( số hạng )
Tổng của dãy số trên là:
( 59 + 13 ) x 24 : 2 = 864
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\(\dfrac{5}{6}\cdot\dfrac{1}{3}+\dfrac{1}{2}\cdot\dfrac{3}{4}\cdot\dfrac{5}{3}\)
\(=\dfrac{5\cdot1}{6\cdot3}+\dfrac{1}{2}\cdot\dfrac{3\cdot5}{4\cdot3}\)
\(=\dfrac{5}{18}+\dfrac{1}{2}\cdot\dfrac{15}{12}\)
\(=\dfrac{5}{18}+\dfrac{1}{2}\cdot\dfrac{5}{4}\)
\(=\dfrac{5}{18}+\dfrac{1\cdot5}{2\cdot8}\)
\(=\dfrac{5}{18}+\dfrac{5}{8}\)
\(=\dfrac{65}{72}\)
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\(\dfrac{5}{6}.\dfrac{1}{3}+\dfrac{5}{6}+\dfrac{3}{4}\)
\(=\dfrac{5}{6}.\left(\dfrac{1}{3}+\dfrac{3}{4}\right)=\dfrac{5}{6}.\dfrac{7}{12}=\dfrac{35}{72}\)
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a) {[( 32 + 1 ) . 10 - ( 8 : 2 + 6 ) ] : 2 } + 55 -( 10 : 5 )3
= ( 10 . 10 - 10 : 2 ) + 55 - 6
= 90 : 2 ) + 55 - 6
= 45 + 55 - 6
= 100 - 6
= 94
b) 100 - [ 60 - ( 9 - 2 )2 ] . 32
= 100 - [ 60 - 72 ] . 9
= 100 - [ 60 - 49 ] . 9
= 100 - 11 . 9
= 100 - 99
= 1
c) [ ( 1253 ) . 75 - ( 175 )5 : 5 ] : 20162017
= 0 : 20162017
= 0
+ bài d kg hiểu! Xin lỗi
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a) -187 + (-1907) - ( 1706 - 619 - 581 )
= -187 + (-1907) - 1706 + 619 + 581
= -187 +(-1907) + (-1706) + 619 + 581
= [-187 + (-1907) + (-1706)] + (619 +581)
= -3800 + 1200
= -2600
b) 1 - 2 - 3 + 4 + 5 - 6 - 7 + 8 +.....+ 2013 - 2014 - 2015 +2016
= (1-2-3+4) + (5-6-7+8) + .............+ (2013-2014-2015+2016)
=0 + 0 +.........+0
=0
a) -187 + (-1907) - ( 1706 - 619 - 581 )
=-187 + (-1907) -1706 + 619 + 581
=........
=.....
=-3800 + 1200
=-2600
b) 0
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\(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{-5}{7}+\dfrac{1}{6}-\dfrac{3}{35}+\dfrac{1}{3}-\dfrac{-1}{41}\)
\(=\left(\dfrac{1}{2}+\dfrac{1}{3}+\dfrac{1}{6}\right)+\left(-\dfrac{1}{5}-\dfrac{5}{7}-\dfrac{3}{35}\right)+\dfrac{1}{41}\)
\(=\dfrac{3+2+1}{6}+\dfrac{-7-25-3}{35}+\dfrac{1}{41}\)
\(=\dfrac{6}{6}+\dfrac{-35}{35}+\dfrac{1}{41}=\dfrac{1}{41}\)
S=1+5+5^2+5^3+..+5^2016
5S=5(1+5+5^2+5^3+..+5^2016)
5S=5+5^2+5^3+5^4+..+5^2017
=>5S-S=(5+5^2+5^3+5^4+..+5^2017)-(1+5+5^2+5^3+...+5^2016)
4S=5^2017-1
S=(5^2017-1)/4
5S=5+5^2+5^3+...+5^2017
4S=(5+5^2+5^3+...+5^2017)-(1+5+5^2+...+5^2016)
4S=5^2017-1(cho này hơi khó hiểu bạn nên đoc kì lại)
S=5^2017-1
4