1 tính : 6. 8 -2.3
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Những câu hỏi liên quan
CB
1
4 tháng 8 2015
a) \(A=\frac{1}{8}+\frac{1}{24}+\frac{1}{48}+...+\frac{1}{10200}\)
\(A=\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+...+\frac{1}{100.102}\)
\(2A=\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{100.102}\)
\(2A=\left(\frac{1}{2}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{6}\right)+\left(\frac{1}{6}-\frac{1}{8}\right)+...+\left(\frac{1}{100}-\frac{1}{102}\right)\)
\(2A=\frac{1}{2}-\frac{1}{102}\)
\(2A=\frac{25}{51}\)
\(A=\frac{25}{51}:2\)
\(A=\frac{25}{102}\)
Vậy \(\frac{1}{8}+\frac{1}{24}+\frac{1}{48}+...+\frac{1}{10200}=\frac{25}{102}\)
b) \(B=\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{2015.2016}\)
\(B=3.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2015.2016}\right)\)
\(B=3.\left[\left(\frac{1}{1}-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{3}\right)+\left(\frac{1}{3}-\frac{1}{4}\right)+...+\left(\frac{1}{2015}-\frac{1}{2016}\right)\right]\)
\(B=3.\left(\frac{1}{1}-\frac{1}{2016}\right)\)
\(B=3.\frac{2015}{2016}\)
\(B=\frac{2015}{672}\)
Vậy \(\frac{3}{1.2}+\frac{3}{2.3}+\frac{3}{3.4}+...+\frac{3}{2015.2016}=\frac{2015}{672}\)
K
1
6 tháng 1 2016
A = 1 - 2.32 + 2(12 -32)
A = 1 - 2.32 + 2.12 - 2.32
A = 1 + (-2.32 - 2.32) + 2.12
A = 1 + (-36) + 24 = 11
B = 2 - 4 + 6 - 8 + .... + 98 - 100
B = (2 - 4) + (6 - 8) + .... + (98 x 100)
B = 2 + 2+ ....... + 2
B = 2 x 25 = 50
S
5
31 tháng 1 2016
a ta co ;
13 -12 +11+10-9+8-7-6+5-4+3+2-1
=13-(12-11-10+9) +(8-7-6+5) -(4-3-2+1)
= 13 -0+0 -0
=13
MN
26 tháng 3 2021
a) 32 - 6 . (8 - 23) + 18 = 32 - 6 . (8 - 8) + 18
= 32 - 6 . 0 + 18 = 32 + 18 = 50
b) (3 . 5 - 9)3 . (1 + 2 . 3)2 + 42
= (15 - 9)3 . (1 + 6)2 + 42
= 63 . 72 + 42 = 216 . 49 + 16 = 10 584 + 16 = 10 600
6 tháng 7 2019
a) Đặt A = 1/2 + 1/4 + 1/8 + 1/16 + 1/32
A = 1/2 + 1/22 + 1/23 + 1/24 + 1/25
2A = 2(1/2 + 22 + 1/23 + 1/24 + 1/25)
2A = 1 + 1/2 + 1/22 + 1/23 + 1/24
2A - A = (1 + 1/2 + 1/22 + 1/23 + 1/24) - (1/2 + 1/22 + 1/23 + 1/24 + 1/25)
A = 1 - 1/25
A = 31/32
b) 2/1.2 + 2/2.3 + 2/3.4 + ... + 2/18 . 19 + 2/19.20
= 2(1/1.2 + 1/2.3 + 1/3.4 + ... + 1/18.19 + 1/19.20)
= 2.(1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/18 - 1/19 + 1/19 - 1/20)
= 2. (1 - 1/20)
= 2.19/20
= 19/10
5 tháng 4 2018
\(A=\frac{1\cdot2+2\cdot3+3\cdot4+...+20\cdot21}{1+2-3-4+5+6-7-8+...+197+198-199-200+201}\) (1)
đặt \(B=1\cdot2+2\cdot3+3\cdot4+...+20\cdot21\)
\(3B=1\cdot2\cdot3+2\cdot3\cdot3+3\cdot4\cdot3+...+20\cdot21\cdot3\)
\(3B=1\cdot2\cdot\left(3-0\right)+2\cdot3\cdot\left(4-1\right)+3\cdot4\cdot\left(5-2\right)+...+20\cdot21\cdot\left(22-19\right)\)
\(3B=1\cdot2\cdot3+2\cdot3\cdot4-1\cdot2\cdot3+3\cdot4\cdot5-2\cdot3\cdot4+...+20\cdot21\cdot22-19\cdot20\cdot21\)
\(3B=20\cdot21\cdot22\)
\(B=\frac{20\cdot21\cdot22}{3}=3080\) (2)
đặt \(C=1+2-3-4+5+6-7-8+...+197+197-199-200+201\)
\(C=\left(1+2-3-4\right)+\left(5+6-7-8\right)+...+\left(197+198-199-200\right)+201\)
\(C=-4+\left(-4\right)+...+\left(-4\right)+201\) có 50 số -4
\(C=-4\cdot50+201\)
\(C=-200+201\)
\(C=1\) (3)
\(\left(1\right)\left(2\right)\left(3\right)\Rightarrow A=\frac{B}{C}=\frac{30801}{1}=3080\)
NK
3 tháng 1 2016
S = 1.2 + 2.3 + 3.4 +...+99.100
3S = 1.2.3 + 2.3.(4 - 1) + 3.4(5 - 2) +...+ 99.100(101 - 98)
3S = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 +...+ 99.100.101 - 98.99.100
3S = 99.100.101
3S = 999900
S = 333300
P = 1 + 3 + 5 + 7 +...+ 2015
P = (2015 + 1)1008 : 2
P = 1016064
T = 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 +...+ 97 + 98 - 99 - 100
T = (1 + 2 - 3 - 4) + (5 + 6 - 7 - 8) +...+ (97 + 98 - 99 - 100)
T = (-4) + (-4) +...+ (-4)
T = (-4)25
T = -100
6. 8 - 2 . 3
=48 - 6
= 42
8.5 nhé bạn