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a) (x-14):2=24-3
(x-14):2 = 13
x-14 = 13.2
x-14 = 26
x = 26 + 14
x = 40
b) x572 = x <=> x = 1 hoặc 0
a, b làm như trên nha, còn mấy bìa còn lại :
M=1+2+22+...+211
M = \(\left(1+2+2^2+2^3+2^4+2^5\right)+\left(2^6+2^7+2^8+2^9+2^{10}+2^{11}\right)\)
M = (1+2+4+8+16+32) + 26( 1 + 2 + 22+23+24+25)
M = 63 + 26.63
M = 63 ( 1+ 26)
M= 9.7 (1 + 2^6) chia hết cho 9 => M chia hết cho 9
S=3 + 32 +33 +.....+ 39
S = \(\left(3+3^2+3^3\right)+\left(3^4+3^5+3^6\right)+\left(3^7+3^8+3^9\right)\)
S = \(3\left(1+3+3^2\right)+3^4\left(1+3+3^2\right)+3^7\left(1+3+3^2\right)\)
S= 3. 13 + 3^4.13 + 3^7.13
S= 13 ( 3 +3^4+3^4) chia hết cho 13 => S chia hết cho 13
M= 2+ 22 + 23+....+210
M= \(\left(2+2^2\right)+\left(2^3+2^4\right)+...+\left(2^9+2^{10}\right)\)
M = \(2\left(1+2\right)+2^3\left(1+2\right)+...+2^9\left(1+2\right)\)
\(M=2.3+2^3.3+...+2^9.3\)
M = 3( 2+ 2^3 +...+ 2^9) chia heets cho 3
=> M chia hết cho 3
A= 7+ 72 + 73 +.....+78
A= \(\left(7+7^2+7^3+7^4\right)+\left(7^5+7^6+7^7+7^8\right)\)
A= \(7\left(1+7+7^2+7^3\right)+7^5\left(1+7+7^2+7^3\right)\)
A= 7. 400 + 7^5 . 400
A = 400( 7+7^5)
A = 5 . 80 ( 7+7^5) chia hết cho 5 => A chia hết cho 5
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
A = ( 2+22+23) + (24+25+26) + (27+28+29)+ (210+211+212)
A = 2.(1+2+22) +24.(1+2+22) +27.(1+2+22)+ 210.(1+2+22)
A = 2.7+24.7 +27.7+ 210.7
A = 7.( 2+24+27+210)
Suy ra A chia hết cho 7
A=2+22+23+24+25+26+27+28+29+210+211+212
=2(1+2+22)+24(1+2+22)+27(1+2+22)+210(1+2+22)
=2.7+2.7+2.7+2.7
Vậy A chia hết cho 7
6) \(2\left(x-8\right)=2^2\)
\(\Rightarrow x-8=2^2:2\)
\(\Rightarrow x-8=2\)
\(\Rightarrow x=2+8\)
\(\Rightarrow x=10\)
tíc mình nha
5) 14 chia hết cho 2x+3
=>2x+3 thuộc ước 14
mà Ư(14)={1,2,7,14}
ta có
| 2x+3 | 1 | 2 | 3 | 14 |
| x | X | X | 0 | X |
vậy x=0
a) 120 - 5 . ( x + 2 ) = 45
5 . (x + 2) = 120 - 45
5 . (x + 2) = 75
x + 2 = 75 : 5
x + 2 = 15
x = 17
b) ( 2.x - 3 )2 = 49
( 2.x - 3 )2 = 72
( 2.x - 3 ) = 7
2x = 10
x = 5
\(\left[\left(6x-72\right):2-84\right].28=5628\)
\(\Rightarrow\left[\left(6x-72\right):2-84\right]=201\)
\(\Rightarrow\left[\left(6x-72\right):2\right]=285\)
\(\Rightarrow6x-72=570\)
\(\Rightarrow6x=642\)
\(\Rightarrow x=107\)
\(A=2+2^2+2^3+2^4+...+2^{10}\)
\(A=\left(2+2^2\right)\left(2^3+2^4\right)+...+\left(2^9+2^{10}\right)\)
\(A=3.2+3.2^3+3.2^5+...+3.2^9\)
\(A=3\left(2+2^3+2^5+...+2^9\right)⋮3\)
Vậy A chia hết cho 3