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Cau a la ban hay tinh trong dau ngoac don truoc sau do lam nhoac vuong va lam dau ngoac nhon va tinh cac phep tinh con lai
\(G=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+..............+\frac{1}{3^{100}}\)
\(3G=1+\frac{1}{3}+\frac{1}{3^2}+...............+\frac{1}{3^{99}}\)
\(3G-G=\left(1+\frac{1}{3}+\frac{1}{3^2}+..........+\frac{1}{3^{99}}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...............+\frac{1}{3^{100}}\right)\)
\(2G=1-\frac{1}{3^{100}}\)
\(\Rightarrow G=\left(1-\frac{1}{3^{100}}\right):2\)
2.
a,\(50-\left[\left(50-2^3.5\right):2+3\right]\)
\(=50-\left[\left(50-40\right):2+3\right]\)
\(=50-\left(10:2+3\right)\)
\(=50-8\)
\(=42\)
b,\(8697-\left[3^7:3^5+2\left(13-3\right)\right]\)
\(=8697-\left(3^2+2.10\right)\)
\(=8697-\left(9+20\right)\)
\(=8697-29\)
\(=8668\)
c,\(205-\left[1200-\left(4^2-2.3\right)^3\right]:40\)
\(=205-200:40\)
\(=200\)
2)
a) \(50-\left[\left(50-2^3.5\right):2+3\right]\)
\(=50-\left[\left(50-8.5\right):2+3\right]\)
\(=50-\left[\left(50-40\right):2+3\right]\)
\(=50-\left(10:2+3\right)\)
\(=50-\left(5+3\right)\)
\(=50-8\)
\(=42\)
b) \(8697-\left[3^7:3^5+2\left(13-3\right)\right]\)
\(=8697-\left(3^7:3^5+2.10\right)\)
\(=8697-\left(3^{7-5}+2.10\right)\)
\(=8697-\left(3^2+2.10\right)\)
\(=8697-\left(9+2.10\right)\)
\(=8697-\left(9+20\right)\)
\(=8697-29\)
\(=8668\)
c) \(205-\left[1200-\left(4^2-2.3\right)^3\right]:40\)
\(=205-\left[1200-\left(16-2.3\right)^3\right]:40\)
\(=205-\left[1200-\left(16-6\right)^3\right]:40\)
\(=205-\left(1200-10^3\right):40\)
\(=205-\left(1200-1000\right):40\)
\(=205-200:40\)
\(=205-5\)
\(=200\)
a) 205 – [1200 – (42 – 2.3)3] : 40
= 205 – [1200 – ( 16 - 6 )3 ] : 40
= 205 – [1200 – ( 10 )3 ] : 40
= 205 – [1200 – 1000 ] : 40
= 205 – 200 : 40
= 205 – 50
= 155
b) 177 :[2.(42 – 9) + 32(15 – 10)]
= 177 :[2.(16 – 9) + 9. 5]
= 177 :[2.7 + 9. 5]
= 177 :[ 14 + 45 ]
= 177 : 59
= 3
= 1200 - (1500 . 2 + 1800 . 3 + 1800 . 2 : 3)
= 1200 - (1500 . 2 + 900 . 2 . 3 + 1800 : 3 . 2)
= 1200 - (1500 . 2 + 2700 . 2 + 600 . 2)
= 1200 - [2 . (1500 + 2700 + 600)]
= 1200 - (2 . 4800)
= 1200 - 9600
= -8400
= 205 - [(1200 - (16 - 2 . 3)3 ] : 40
= 205 - [1200 - (16 - 6)3 ] : 40
= 205 - [1200 - 103 ] : 40
= 205 - [1200 - 1000 ] : 40
= 205 - 200 : 40
= 205 - 5
= 200
Tick nha bạn
205 - [(1200 - (42 - 2 . 3)3 ] : 40
= 205 - [(1200 - (16 - 2 . 3)3 ] : 40
= 205 - [1200 - (16 - 6)3 ] : 40
= 205 - [1200 - 103 ] : 40
= 205 - [1200 - 1000 ] : 40
= 205 - 200 : 40
= 205 - 5
= 200
a . ( 2600 + 6400 ) - 3 . x = 1200
=>9000-3x=1200
=>3x=9000-1200
=>3x=7800
=>x=7800:3
=>x=2600
vậy x=2600
b . [ ( 6 . x - 72 ) : 2 - 84 ] . 28 = 5628
=>
( 6 . x - 72 ) : 2 - 84=5628:28
( 6 . x - 72 ) : 2 - 84=201
=>6x-72=(201+84).2
=>6x-72=570
=
>6x=570+72
=>6x=642
=>x=642:6
=>x=107
vậy x=107
A = 2 + 22 + 23 + 24 + ... + 210
A=(2+22)+22.(2+22)+...+28.(2+22)
A=6+22.6+......+28.6
A=6.(1+22+...+28)
Mà 6 chia hết cho 3
=>6.(1+22+...+28) chia hết cho 3
=>A chia hết cho 3
bài 204
a) (2600+6400)-3.x=1200
=>9000-3.x=1200
=>3.x=7800
=>x=2600
b)[(6.x-72):2-84].28=5628
[(6.x-72):2-84]=201
(6.x-72):2=285
6.x-72=570
6.x=642
x=107
\(1200-2^3+10^3\)
=1200-8+1000
=2200-8=2192
1200-23 +103
=1200-8+1000
=1192+1000
=2192