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![](https://rs.olm.vn/images/avt/0.png?1311)
x+[x+1]+[x+2]+...........+[x+30]=1240
[x+x+x+...+x]+(0+1+2+3+...+30)=1240
Từ 0 đến 30 có 31 số lên sẽ có 31 số x
Vậy: x.31+(0+1+2+3+...+30)=1240
x.31+((30+0)x31:2)=1240
x.31+30x31:2=1240
x.31 + 465 =1240
x.31 =1240-465=775
X=775:31
X=25
Vậy x =25
1.2.3........8.9-1.2.3.........8-1.2.3........7.8 2
=1.2.3....8.(9-1-1.2.3....7.8)
=40320.(-40312)
=-1625379840
nhé Nguyễn Trà My
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
A,
(100+121+144)÷(169+196)
=365:365=1
B
,1.2.3...7.8.(9-1-8)
=1.2.3...7.8.0=0
C,
3^2.2^4.2^32/11.2^13.2^22-2^26
=3^2.2^36/11.2^35-2^36
=3^2.2^36/2^35-(11-2)
=9.2/9=2
D,
=1152-374-1152+(-65)+374
=(1152-1152)+(-374+374)+(-65)
=0+0+(-65)=-65
E,
=13-(12-11-10+9)+(8-7-6+5)-(4-3-2+1)
=13-0+0-0=13
Bài 2:
A,(19x+50)÷14=25-16
(19x+50)÷14=9
19x+50=126
19x=76
x=4
B,
31x+(1+2+3+...+30)=1240
31x+465=1240
31x=775
×=25
![](https://rs.olm.vn/images/avt/0.png?1311)
cau b ta co9;(x+x+.....+x)-(1+2+....+100)=4950
100x - 5050 =4950
100x =4950+5050
100x =10000
x=10000 ;100
x=100
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(1.2.3....9-1.2.3...8-1.2.3...7.8^2\)
\(=1.2.3....8.\left(9-1-8\right)\)
\(=1.2.3...8.0\)
\(=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài làm
1.2.3...9 - 1.2.3...8 - 1.2.3...7.82
= 1.2.3...8.( 9 - 1 - 8 )
= 1.2.3...8 .0
= 0
_Chúc_Bạn_Hok_Tốt_^^
\(1.2.3....9-1.2.3...8-1.2.3...7.8^2=1.2.3....8\left(9-1-8\right)=1.2.3....8.0=0\)
![](https://rs.olm.vn/images/avt/0.png?1311)
1.2.3.......9-1.2.3...8-1.2.3....82
=1.2.3.......9-1.2.3.........8-1.2.3....8.8
= 1.2.3....8(9-1-8)
=1.2.3......8.0
=0
1.
= 1.2...8.( 9 + 1 +8)
= 40320.18
= 725760
2.
⇒ (x + x+..+ x)+ (0 + 1 + 2 +...+ 30) =1240
từ 0 đến 30 có tất cả 31 số vậy có 31 số hạng x
áp dụng công thức gauss ta có 0+1+..+n = \(\dfrac{n\left(n+1\right)}{2}\)
⇒ 31x + 465 = 1240
⇒ 31x = 775
⇒ x = 25
Vậy x = 25
Câu 1:
\(1.2.3.....9-1.2.3.....8-1.2.3.....7.8^2.\)
\(=8!\left(9-8-8^2\right).\)
\(=40320.\left(-63\right).\)
\(=-2540160.\)
Vậy..........
Câu 2:
\(x+\left(x+1\right)+\left(x+2\right)+\left(x+3\right)+...+\left(x+30\right)=1240.\)
\(x+x+1+x+2+x+3+...+x+30=1240.\)
\(\left(x+x+x+...+x\right)+\left(1+2+3+...+30\right)=1240.\)
\(31x+465=1240.\)
\(31x=1240-465.\)
\(31x=775.\)
\(x=\dfrac{775}{31}.\)
\(x=25.\)
Vậy..........