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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
a)2.18.14+3.17.12+4.69.9
=(2.18).14+(12.3).17+(4.9).69
=36.14+36.17+36.69
=36.(14+17+69)
=36.100
=3600
b)1+(-3)+5+(-7)+9+(-11)+13+(-15)
=[1+(-3)]+[5+(-7)]+[9+(-11)]+[13+(-15)]
=(-2)+(-2)+(-2)+(-2)
=(-8)
\(\left(13\frac{4}{9}+2\frac{1}{9}\right)-3\frac{4}{9}\)
\(=\left(\frac{121}{9}+\frac{19}{9}\right)-\frac{31}{9}\)
\(=\frac{140}{9}-\frac{31}{9}\)
\(=\frac{109}{9}\)
\(1,25\div\frac{15}{20}+\left(25\%-\frac{5}{6}\right)\div4\frac{2}{3}\)
\(=1,25\div\frac{3}{4}+\left(\frac{25}{100}-\frac{5}{6}\right)\div\frac{14}{3}\)
\(=1,25\times\frac{4}{3}+\left(\frac{6}{24}-\frac{20}{24}\right)\div\frac{14}{3}\)
\(=\frac{5}{3}+\frac{-14}{24}\times\frac{14}{3}\)
\(=\frac{60}{36}+\frac{-98}{36}\)
\(=\frac{-38}{36}=\frac{-19}{18}\)
Câu a:
A = 7 2/13 - (5 2/13 + 2 1/2)
A = 7 2/13 - 5 2/13 - 2 1/2
A = 2 - 2 1/2
A = 2 - 2 - 1/2
A = 0 - 1/2
A = -1/2
Câu b:
B = - 3/4 + 25% : (10 3/10 - 9 4/5) - (-1/2)^2
B = - 3/4 + 1/4 : (103/10 - 49/5) - 1/4
B = - 3/4 + 1/4 : (103/10 - 98/5) - 1/4
B = (-3/4 - 1/4) + 1/4 : (1/2)
B = -1 + 1/4 x 2/1
B = -1 + 1/2
B = - 1/2
Câu a:
A = 7 2/13 - (5 2/13 + 2 1/2)
A = 7 2/13 - 5 2/13 - 2 1/2
A = 2 - 2 1/2
A = 2 - 2 - 1/2
A = 0 - 1/2
A = -1/2
Câu b:
B = - 3/4 + 25% : (10 3/10 - 9 4/5) - (-1/2)^2
B = - 3/4 + 1/4 : (103/10 - 49/5) - 1/4
B = - 3/4 + 1/4 : (103/10 - 98/5) - 1/4
B = (-3/4 - 1/4) + 1/4 : (1/2)
B = -1 + 1/4 x 2/1
B = -1 + 1/2
B = - 1/2
b: =12+5/14-3-5/7-5-5/14
=4-5/7
=28/7-5/7=23/7
c: =(-2/5-11/10)+(7/11-7/11)
=-4/10-11/10=-15/10=-3/2
\(a,\dfrac{5}{9}\cdot\dfrac{7}{13}+\dfrac{5}{9}\cdot\dfrac{8}{13}-\dfrac{5}{13}\cdot\dfrac{2}{9}\)
\(=\dfrac{5}{9}\cdot\dfrac{7}{13}+\dfrac{5}{9}\cdot\dfrac{8}{13}-\dfrac{2}{13}\cdot\dfrac{5}{9}\)
\(=\dfrac{5}{9}\cdot\left(\dfrac{7}{13}+\dfrac{8}{13}-\dfrac{2}{13}\right)\)
\(=\dfrac{5}{9}\cdot\dfrac{14}{13}\)
\(=\dfrac{70}{117}\)
\(d,\dfrac{1}{2}+\dfrac{-2}{3}+\dfrac{1}{6}+\dfrac{-2}{5}\)
\(=\left(\dfrac{1}{2}+\dfrac{-2}{3}+\dfrac{1}{6}\right)+\dfrac{-2}{5}\)
\(=0+\dfrac{-2}{5}\)
\(=\dfrac{-2}{5}\)
a) (-124) + 24 = -100
b) 37. 78 + 37. 22
= 37 . ( 78 + 22 )
= 37 . 100
= 3700
Số số hạng của dãy là : (397−1):4+1=100(397-1):4+1=100 ( số )
⇒⇒ Có 100:2=50100:2=50 ( cặp )
1−5+9−13+....+393−3971-5+9-13+....+393-397
=(1−5)+(9−13)+....+(393−397)=(1-5)+(9-13)+....+(393-397)
=(−4)+(−4)+....+(−4)=(-4)+(-4)+....+(-4)
=(−4).50=−200=(-4).50=-200
TK`1-5+9-13+...+393-397`
`=(1-5)+(9-13)+...+(393-397)` (197 cặp)
`=(-4)+(-4)+...+(-4)`
`=(-4) xx 197`
`=-788`
1-5+9-13+...+393-397
=(-4)+(-4)+...+(-4)
=(-4)*100
=-400
Thanks
á mik nhầm:(-4)*25=-100
50 cặp nkaaaaa.
(-4) x 50 = -200
50 cặp mới đúng nhé
(393-1):8+1=50 nhé
-4.50=-200
thì 50 cặp ĐC CHX???????????????///////
Cảm ơn nha
Giải:
1-5+9-13+...+393-397
=(1-5)+(9-13)+...+(393-397)
=(-4)+(-4)+...+(-4)
Vì:
Số số hạng: (397-1):4+1=100
⇒Có: 100:2=50 (cặp)
=(-4).50
=-200
Chúc bạn học tốt!
Thanks