Tính nhanh
a)A = 1 + 1/2 +1/4 + .......+ 1/2^99 +1/2^100+1/2^100
b) 12/56 + 12/140+12/260 +.....+ 12/1400
Những câu hỏi liên quan
Đề Bài: Tính:
a) B bằng 1/6+ 1/12+ 1/20+ 1/42+ 1/56+ 1/72+ 1/90
b) C bằng 10/56+ 10/140+ 10/260+...+ 10/1400
Tính nhanh :
a)13 – 12 + 11 + 10 – 9 + 8 – 7 – 6 + 5 – 4 + 3 + 2 – 1
b) 10/56 + 10/140 + 10/260 + ... + 10/2400
c) 1/1. 2. 3 + 1/2. 3. 4 + 1/3. 4. 5 + ... + 1/18. 19. 20
Tính nhanh: a.(1-1/2)(1-1/3)(1-1/4)...(1-1/100)
b. 10/56+10/140+10/260+.....+10/1400
Các bạn giải giùm mình nhanh nhanh được k? Mình đang cần gấp
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Bài 1: Tính K =\(\frac{10}{56}+\frac{10}{140}+\frac{10}{260}\)+...+\(\frac{10}{1400}\)
Bài 2: Cho M =\(\frac{1}{2}+\frac{1}{12}+\frac{1}{30}+...+\frac{1}{9900}\).CMR: M<\(\frac{5}{6}\).
1tính tổng
A =(1-1/2)+(1-1/6)+(1-1/12)+..+(1-1/70)
B=(1-1/3)+(1-1/15)+(1-1/35)+(1-1/63)
C=1/2+5/6+11/12+....+8998/9900
D=2/3+14/15+34/35+...+1119/1120
E=9/10+39/40+87/88+....+9998/9999
F=10/56+10/140+10/260+...+10/1400
G=1/1.2.3+1/2.3.4+1/3.4.5+1/+4.5.6+...+1/8.9.10
H=2/2007+2/60.63+2/63.66+...+2/117.120
I=1-1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2
mình cần gấp mông mọi người giúp nha !
12/56 + 12/140 + 12/260 + ... + 12/1400
Nhanh nhanh giúp mk nhé! Ai làm đúng mk tik cho!
Tính:\(\frac{12}{56}+\frac{12}{140}+\frac{12}{260}+...+\frac{12}{1400}\)
Ta đặt phép tính trên là A
A=12/56+12/140+12/260+....+12/1400
A=6/28+6/70+6/130+...+6/700 3/6
A=3/28+3/70+3/130+....+3/700 3/6.
A=3/4.7+3/7.10+3/10.13+....+3/25.28 3/6
.A=1/4-1/7+1/7-1/10+1/10-1/13+...+1/25-1/28 3/6.
A=(1/4-1/28)+(1/7-1/7)+(1/10+/10)+..+(1/25-1/28) 3/6.
A=7/28-1/28+0+0+...+0 3/6.A=3/14
A=3/14:3/6 A=3/14.6/3 A=3/7
Vậy GTBT=3/7
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12/56 + 12/140 + 12/260 + ... + 12/1400
= 5/28 + 5/70 + 5/130 + ... + 5/700
= 5/3 x ( 3/4x7 + 3/7x10 + 3/10x13 + ... + 3/25x28 )
= 5/3 x ( 1/4 - 1/7 + 1/7 - 1/10 + 1/10 - 1/13 + ... + 1/25 - 1/28 )
= 5/3 x ( 1/4 - 1/28 )
= 5/3 x 3/14
= 5/14
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ta đặt phép tính trên là A
A=12/56+12/140+12/260+....+12/1400
A=6/28+6/70+6/130+...+6/700
3/6.A=3/28+3/70+3/130+....+3/700
3/6.A=3/4.7+3/7.10+3/10.13+....+3/25.28
3/6.A=1/4-1/7+1/7-1/10+1/10-1/13+...+1/25-1/28
3/6.A=(1/4-1/28)+(1/7-1/7)+(1/10+/10)+..+(1/25-1/28)
3/6.A=7/28-1/28+0+0+...+0
3/6.A=3/14
A=3/14:3/6
A=3/14.6/3
A=3/7
Vậy GTBT=3/7
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tính tổng:
a) A = 1/3 + 1/3^2 + 1/3^3 +........+ 1/3^100
b) B = 10/56 + 10/140 + 10/260 +.....+ 10/1400
mọi người giúp mk vs
ai làm đc 1 trong 2 câu nhanh nhất mk sẽ tk cho
THANKS
\(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{100}}\)
\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{99}}\)
\(3A-A=\left(1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{99}}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{100}}\right)\)
\(2A=1-\frac{1}{3^{100}}\)
\(A=\frac{1-\frac{1}{3^{100}}}{2}\)
\(B=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)
\(B=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}\)
\(B=\frac{5}{4.7}+\frac{5}{7.10}+\frac{5}{10.13}+...+\frac{5}{25.28}\)
\(3B=\frac{5.3}{4.7}+\frac{5.3}{7.10}+\frac{5.3}{10.13}+...+\frac{5.3}{25.28}\)
\(3B=5\left(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+...+\frac{3}{25.28}\right)\)
\(3B=5\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\right)\)
\(3B=5\left(\frac{1}{4}-\frac{1}{28}\right)\)
\(3B=5\cdot\frac{3}{14}=\frac{15}{14}\)
\(B=\frac{15}{14}:3=\frac{5}{14}\)
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a) \(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{100}}\)
\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{99}}\)
\(3A-A=\left(1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{99}}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{100}}\right)\)
\(2A=1-\frac{1}{3^{100}}\)
\(\Rightarrow A=\frac{1-\frac{1}{3^{100}}}{2}\)
b) \(B=\frac{10}{56}+\frac{10}{140}+\frac{10}{260}+...+\frac{10}{1400}\)
\(B=\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+...+\frac{5}{700}\)
\(B=\frac{5}{4.7}+\frac{5}{7.10}+\frac{5}{10.13}+...+\frac{5}{25.28}\)
\(B=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{7}\right)+\frac{5}{3}.\left(\frac{1}{7}-\frac{1}{10}\right)+\frac{5}{3}.\left(\frac{1}{10}-\frac{1}{13}\right)+...+\frac{5}{3}.\left(\frac{1}{25}-\frac{1}{28}\right)\)
\(B=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+...+\frac{1}{25}-\frac{1}{28}\right)\)
\(B=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{28}\right)\)
\(B=\frac{5}{3}.\frac{3}{14}\)
\(\Rightarrow B=\frac{5}{14}\)
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\(A=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...+\frac{1}{3^{100}}\)
\(3A=1+\frac{1}{3}+\frac{1}{3^2}+...+\frac{1}{3^{99}}\)
\(3A-A=1-\frac{1}{3^{100}}\)\(\Rightarrow2A=\left(1-\frac{1}{3^{100}}\right)\Rightarrow A=\frac{1}{2}\times\left(1-\frac{1}{3^{100}}\right)\)
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tính nhanh
a,(1-1/10)+(1-1/11)+(1-1/12)+...+(1-1/99)+(1-1/100)
b,1/2*3+1/2*4+1/4*5+...+1/99*100