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1.4x - 5(-3+x)=7
4x - 5(x-3) =7
4x - 5x + 15=7
-1x + 15=7
-1x =-8
=> x =8
2.5(x-3) - 2(x+6)=9
5x - 15 -2x -12=9
5x - 2x -15 - 12=9
5x - 2x=9 + 12 + 15
5x - 2x= 36
3x = 36
=> x = 12
3.4(x-1) - 3(x-2)=15
4x - 4 - 3x + 6=15
4x - 3x =15 - 6 + 4
4x - 3x = 13
=> x = 13
Nhớ mink nhoa pn
![](https://rs.olm.vn/images/avt/0.png?1311)
a) Ta có: \(\dfrac{39}{-65}=\dfrac{-39}{65}=\dfrac{-39:13}{65:13}=\dfrac{-3}{5}\)
\(\dfrac{-3}{5}=\dfrac{-3}{5}\)
Do đó: \(\dfrac{-3}{5}=\dfrac{39}{-65}\)
b) Ta có: \(\dfrac{-9}{27}=\dfrac{-9:9}{27:9}=\dfrac{-1}{3}\)
\(\dfrac{-41}{123}=\dfrac{-41:41}{123:41}=\dfrac{-1}{3}\)
Do đó: \(\dfrac{-9}{27}=\dfrac{-41}{123}\)
c) Ta có: \(\dfrac{-3}{4}=\dfrac{-3\cdot5}{4\cdot5}=\dfrac{-15}{20}\)
\(\dfrac{4}{-5}=\dfrac{-4}{5}=\dfrac{-4\cdot4}{5\cdot4}=\dfrac{-16}{20}\)
mà \(\dfrac{-15}{20}>\dfrac{-16}{20}\)
nên \(\dfrac{-3}{4}>\dfrac{4}{-5}\)
d) Ta có: \(\dfrac{2}{-3}=\dfrac{-2}{3}=\dfrac{-2\cdot7}{3\cdot7}=\dfrac{-14}{21}\)
\(\dfrac{-5}{7}=\dfrac{-5\cdot3}{7\cdot3}=\dfrac{-15}{21}\)
mà \(\dfrac{-14}{21}>\dfrac{-15}{21}\)
nên \(\dfrac{2}{-3}>\dfrac{-5}{7}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(1-\left(x-1\right):3=\dfrac{2}{3}\)
\(\Rightarrow\left(x-1\right):3=1-\dfrac{2}{3}\)
\(\Rightarrow\left(x-1\right):3=\dfrac{1}{3}\)
\(\Rightarrow x-1=\dfrac{1}{3}.3\)
\(\Rightarrow x-1=1\)
\(\Rightarrow x=2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
( x + 1 ) + ( x + 3 ) + ( x + 5 ) + ( x + 7 ) + ( x + 9 ) bằng bao nhiêu
![](https://rs.olm.vn/images/avt/0.png?1311)
3x+1 + 3x+2 = 324
3x . 3 + 3x . 32 = 324
3x . ( 3 + 32 ) = 324
3x . 12 = 324
3x = 324 : 12
3x = 27
3x = 33
=> x = 3
Vậy x = 3
![](https://rs.olm.vn/images/avt/0.png?1311)
tổng A đã cho có 100 số hạng trừ số hạng đầu tiên thì sẽ được 33 bộ ba như sau:
A = 2 + (2²+2³+2^4) + (2^5+2^6+2^7) +...+ (2^98+2^2^99+2^100)
A = 2 + (2+2²+2³).2 + (2+2²+2³).2^4 +...+ (2+2²+2³).2^97
A = 2 + (2+2²+2³)(2 + 2^4 +..+ 2^97)
A = 2 + 14.(2+2^4 +..+ 2^97) => A chia 7 dư 2
23/6
Đáp số là 23/6 nhé