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( 7 . x - 2 ) . 4 + 13 = 61
( 7 . x - 2 ) . 4 = 61 - 13
( 7 . x - 2 ) . 4 = 48
( 7 . x - 2 ) = 48 : 4
7 . x - 2 = 12
7 . x = 12 + 2
7 . x = 14
x = 14 : 7
x = 2
( 7 . x - 2 ) . 4 + 13 = 61
( 7 . x - 2 ) . 4 = 61 - 13
( 7 . x - 2 ) . 4 = 48
7 . x - 2 = 48 : 4
7 . x - 2 = 12
7 . x = 12 + 2
7 . x = 14
x = 14 : 7
x = 2
Vậy x= 2
( 35 - 2x ) . 4 + 26 = 38
( 35 - 2 . x ) . 4 = 38 - 26
( 35 - 2 . x ) . 4 = 12
( 35 - 2 . x ) = 12 : 4
( 35 - 2 . x ) = 3
2 . x = 35 - 3
2 . x = 32
x = 32 : 2
x = 16
1 . 56- (-23) =56+23 =79
2. 45- 67 = -22
3. -34-59 =-93
4. 81+(-41)=40
( + 56 ) - ( - 23 ) = 79
45 - 67 = -22
- 34 - 59 = - 93
81 + ( - 41 ) = 40
a: \(=\dfrac{3\left(\dfrac{1}{41}-\dfrac{4}{47}+\dfrac{9}{53}\right)}{4\left(\dfrac{1}{47}-\dfrac{4}{47}+\dfrac{9}{53}\right)}=\dfrac{3}{4}\)
b: \(F=2\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+...+\dfrac{1}{2008}-\dfrac{1}{2010}\right)\)
\(=2\cdot\dfrac{1004}{2010}=\dfrac{2008}{2010}=\dfrac{1004}{1005}\)
c: \(S=\dfrac{1}{3\cdot6}+\dfrac{1}{6\cdot9}+...+\dfrac{1}{30\cdot33}\)
\(=\dfrac{1}{3}\left(\dfrac{1}{3}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{9}+...+\dfrac{1}{30}-\dfrac{1}{33}\right)\)
\(=\dfrac{1}{3}\cdot\dfrac{10}{33}=\dfrac{10}{99}\)
4(x+41)=400
=>x+44=400 : 4
x+41=100
=> x=100-41
x=59
\(4\left(x+41\right)=400\)
\(\Rightarrow4x+164=400\)
\(\Rightarrow4x=400-164=236\)
\(\Rightarrow x=236:4=59\)
k mk nhé,sau đó mk sẽ kb vs bn