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Số số hạng là :
\(\left(x-2\right):2+1=x:2-1+1=x:2\) (số hạng)
Tổng trên là :
\(\left(x+2\right).x:2:2=42\)
\(\left(x+2\right).x=42.2.2\)
\(\left(x+2\right).x=168\)
\(\left(x+2\right).x=14.12\)
Vậy x = 14
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`#3107.101107`
a)
\(x+x+\dfrac{1}{2}\times\dfrac{2}{5}+x+\dfrac{8}{10}=121\\3x+\dfrac{1}{5}+\dfrac{4}{5}=121\\ 3x+1=121\\ 3x=121-1\\ 3x=120\\ x=40 \)
Vậy, `x = 40`
b)
\(\dfrac{12+x}{42}=\dfrac{5}{6}\\ \dfrac{12+x}{42}=\dfrac{35}{42}\\ \dfrac{12+x}{42}-\dfrac{35}{42}=0\\ \dfrac{12+x-35}{42}=0\\ \dfrac{x-\left(35-12\right)}{42}=0\\ \dfrac{x-23}{42}=0\\ x-23=0\\ x=23\)
Vậy,` x = 23.`
a: \(x+x+\dfrac{1}{2}\cdot\dfrac{2}{5}+x+\dfrac{8}{10}=121\)
=>\(3x+\dfrac{1}{5}+\dfrac{4}{5}=121\)
=>3x+1=121
=>3x=120
=>x=40
b: \(\dfrac{x+12}{42}=\dfrac{5}{6}\)
=>\(x+12=42\cdot\dfrac{5}{6}=35\)
=>x=35-12=23
![](https://rs.olm.vn/images/avt/0.png?1311)
2 x 3 x 12 + 4 x 6 x 42 + 8 x 27 x 3
= 2 x 12 x 3 + 4 x 6 x 42 + 8 x 3 x 27
= 24 x 3 + 24 x 42 + 24 x 27
= 24 x ( 3 + 42 + 27 )
= 24 x 72
= 1728
2x3x12+4x6x42+8x27x3
=2x3x4x3+4x2x3x42+4x2x27x3
=2x3x4x(3+42+27)
=24x72
=1728
bang 12vi:
2+4+6+8+10+12=42