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a: \(=47-\left[\left(45\cdot16-25\cdot12\right):14\right]\)
\(=47-30=17\)
b: \(=50-\left[6+34\right]\)
=50-40
=10
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
\(G=\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+..............+\frac{1}{3^{100}}\)
\(3G=1+\frac{1}{3}+\frac{1}{3^2}+...............+\frac{1}{3^{99}}\)
\(3G-G=\left(1+\frac{1}{3}+\frac{1}{3^2}+..........+\frac{1}{3^{99}}\right)-\left(\frac{1}{3}+\frac{1}{3^2}+\frac{1}{3^3}+...............+\frac{1}{3^{100}}\right)\)
\(2G=1-\frac{1}{3^{100}}\)
\(\Rightarrow G=\left(1-\frac{1}{3^{100}}\right):2\)
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
B = [1200 - ( 16 - 6 )3 ] : 40
B = [1200 - 103 ] : 40
B = [1200 - 1000] : 40
B = 200 : 40
B = 5
B = [ 1200 - (42 - 2.3)3 ] : 40
B = [ 1200 - (16 - 6)3 ] : 40
B = [ 1200 - 1000]: 40
B = 200: 40
B = 5
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) \(205-\left[1200-\left(4^2-2.3\right)^3\right]:40\)
\(=205-\left[1200-\left(16-2.3\right)^3\right]:40\)
\(=205-\left[1200-\left(16-6\right)^3\right]:40\)
\(=205-\left(1200-10^3\right):40\)
\(=205-\left(1200-1000\right):40\)
\(=205-200:40\)
\(=205-5\)
\(=200\)
\(x+2x+3x+...+15x=\left(x+15x\right)+\left(2x+14x\right)+\left(3x+13x\right)+\left(4x+12x\right)+\left(5x+11x\right)+\left(6x+10x\right)+\left(7x+9x\right)+8x=7.16x+8x=1200\Leftrightarrow x=\dfrac{1200}{7.16+8}=10\)
= 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
\(1200-2^3+10^3\)
=1200-8+1000
=2200-8=2192
1200-23 +103
=1200-8+1000
=1192+1000
=2192