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![](https://rs.olm.vn/images/avt/0.png?1311)
\(1-x=\frac{29}{12}+\frac{32}{8}\)
\(\Rightarrow1-x=\frac{77}{12}\)
\(\Rightarrow x=1-\frac{77}{12}=\frac{-65}{12}\)
\(\frac{31}{8}.x-\frac{11}{4}=\frac{42}{12}.\frac{10}{8}-\frac{1}{3}\)
\(\Rightarrow\frac{31}{8}.x-\frac{11}{4}=\frac{35}{8}-\frac{1}{3}\)
\(\Rightarrow\frac{31}{8}.x-\frac{11}{4}=\frac{97}{24}\)
\(\Rightarrow\frac{31}{8}.x=\frac{97}{24}+\frac{11}{4}=\frac{163}{24}\)
\(\Rightarrow x=\frac{163}{24}:\frac{31}{8}=\frac{163}{93}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
1.Tính :
\(\frac{12}{17}\):6=\(\frac{2}{17}\); 16:\(\frac{8}{11}\)=\(\frac{2}{11}\); 9:\(\frac{3}{5}\)x\(\frac{4}{15}\)=\(\frac{3}{5}\)x\(\frac{4}{15}\)=\(\frac{4}{25}\)
=12/17×1/6
=2/17
=16/1×11/8
=22
9/1×5/3×4/15
15/1×4/15
4/1
![](https://rs.olm.vn/images/avt/0.png?1311)
sửa đề câu a và câu b nhá , mik nghĩ đề như này :
\(\frac{2}{1\cdot3}+\frac{2}{3\cdot5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{213\cdot215}\)
\(=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{213}-\frac{1}{215}\)
= \(\frac{1}{1}-\frac{1}{215}\)
\(=\frac{214}{215}\)
b, đặt \(A=\frac{1}{1\cdot3}+\frac{1}{3\cdot5}+\frac{1}{5\cdot7}+\frac{1}{7\cdot9}+...+\frac{1}{213\cdot215}\)
\(A\cdot2=\frac{2}{1\cdot3}+\frac{2}{3.5}+\frac{2}{5\cdot7}+\frac{2}{7\cdot9}+...+\frac{2}{213\cdot215}\)
\(A\cdot2=\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{213}-\frac{1}{215}\)
\(A\cdot2=\frac{1}{1}-\frac{1}{215}\)
\(A\cdot2=\frac{214}{215}\)
\(A=\frac{214}{215}:2\)
\(A=\frac{107}{215}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a) 1+2+3+...+2018
=[(2018-1):1+1].(2018+1):2
=2018.2019:2
=2037171
b) 4+7+10+13+...+2017
=[(2017-4):3+1].(2017+4):2
=672.2021:2
=679056
c) 1+2-3-4+5+6-7-8+9+10-11-12+13+14
=(1+2-3-4)+(5+6-7-8)+(9+10-11-12)+13+14
=-4+(-4)+(-4)+13+14
=-12+27
=15
d) 23 x 75 + 25 x 23 + 180
=23 x (75+25) +180
=23 x 100 +180
=2300+180
2480
chúc ban hoc tốt nha
a) Số số hạng: ( 2018 - 1 ) : 1 + 1 = 2018
Tổng: 2018 x ( 2018 + 1 ) : 2 = 2 037 171
![](https://rs.olm.vn/images/avt/0.png?1311)
( 54 x 15 ) :9
=54:9x15
=90
( 56 x 23 x 4 ) :7
=56:7x23x4
=8x23x4
=32x23
=736
![](https://rs.olm.vn/images/avt/0.png?1311)
a: =20,23(15,75+85,25-1)
=20,23*100
=2023
b: =4+4=8
c: =6,48(111-1-10)=648
d: =1,25*8*0,25*4
=10
a. 20,23 x 15,75 + 20,23 x 85,25 - 20,23
= 20,23 . (15,75 + 85,25 - 1)
= 20,23 . 100
= 2023
b.0,66 + 1,2+ 3,34+2,8
= 4+4
= 8
c.111 x 6,48 -6,48 - 6,48 x 10
= 6,48 . (111 - 1 -10)
= 648
d.1,25 x 0,25 x 8 x 4
= 1,25 . 8 . 0,25 . 4
= 10
a) 15x9x8x12x5 b)215x62+42-52x215
= (15x8x5)x(9x12) = 215x(62-52)+42
= 600 x108 = 215 x10 +42
=64800 =2150+42
= 2192
a,64800
b,2912
chúc bạn học giỏi