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![](https://rs.olm.vn/images/avt/0.png?1311)
100-200-300-400-500-600-700-800-900-1000=-5300
1000+299-1345-234-345-456-567-678-789-89=-3204
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 1:
a) \(\left(375-180\right):15\)
\(=195:15\)
\(=13\)
b) \(678\left(276+49\right)-678\left(149+76\right)\)
\(=678.325-678.225\)
\(=678\left(325-225\right)\)
\(=678.100\)
\(=67800\)
Bài 2:
\(12:\left\{390:\left[500-\left(125+35.7\right)\right]\right\}\)
\(=12:\left\{390:\left[500-\left(125+245\right)\right]\right\}\)
\(=12:\left\{390:\left[500-370\right]\right\}\)
\(=12:\left\{390:130\right\}\)
\(=12:3\)
\(=4\)
Bài 3:
a) \(2.3^x=54\)
\(\Leftrightarrow3^x=54:2\)
\(\Leftrightarrow3^x=27\)
\(\Leftrightarrow3^x=3^3\)
\(\Leftrightarrow x=3\)
b) \(3^2.3^x=81\)
\(\Leftrightarrow9.3^x=81\)
\(\Leftrightarrow3^x=81:9\)
\(\Leftrightarrow3^x=9\)
\(\Leftrightarrow3^x=3^2=\left(-3\right)^2\)
\(\Leftrightarrow x=2\)
c) \(\left(x-1\right)^3=8\)
\(\Leftrightarrow\left(x-1\right)^3=2^3\)
\(\Leftrightarrow x-1=2\)
\(\Leftrightarrow x=2+1\)
\(\Leftrightarrow x=3\)
Bài 4:
\(A=100+98+96+...+2-97-95-...-1\)
\(\Leftrightarrow A=\left(100+98+96+...+2\right)-\left(97+95+...+1\right)\)
\(\Leftrightarrow A=\left[\left(100+2\right).50:2\right]-\left[\left(97+1\right).49:2\right]\)
\(\Leftrightarrow A=2550-2401\)
\(\Leftrightarrow A=149\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Vì 320 chia hết cho 80 nên mẫu chung của hai phân số là 320.
Ta có:
![](https://rs.olm.vn/images/avt/0.png?1311)
\(5\left(x+60\right)=980-160\)
\(5\left(x+60\right)=820\)
\(x+60=820:5\)
\(x+60=164\)
\(x=104\)
![](https://rs.olm.vn/images/avt/0.png?1311)
x - 200 = 300 + 400
x - 200 = 700
x=700+200
x=900
=> Ta có: 900 - 200 = 300 + 400
x + 100 = 980 - 431
x + 100 = 549
x=549 - 100
x=449
=>Ta có:449 + 100 = 980 - 431
( -500 ) - ( 678 ) + 980
= -1178 + 980
= -198
tích nha
(-500) - 678 + 980
= -1178 + 980
= -198
k nha
thanks you