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`(x+1)+(x+2)+(x+3)+...+(x+9)=945`
`x+1+x+2+x+3+...+x+9=945`
`9x+(1+9)+(2+8)+(3+7)+(4+6)+5=945`
`9x+10+10+10+10+5=945`
`9x+45=945`
`9x=945-45`
`9x=900`
`x=900:9`
`x=100`
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ta thấy có 10 cái ngoặc =>có 10 x
ta có:
(x+x+x+x+....+x) +(1+5+9+13+...+37)=210(có 10 x)
x*10+190=210
x*10=30
x=3
k cho mk nha!
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=9( 1/4.5+1/5.6+...+1/36.37)
=9( 1/4-1/37)... tự yinhs nha
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tìm x :
200 -(2 . x + 6) = 64
2 . x + 6 = 200 - 64
2 . x + 6 = 136
2 . x = 136 - 6
2 . x = 130
x = 130 : 2 = 65
Tính nhanh
1972 - (368 +972)
1972 - 1340
= 632
3345 - 1000 : 192 - 2 . (221 - 218 ) . 3
3345 - ( 1000 ko chia hết cho 192 )
999 + 85 = 1084
( 1 + 37) x 37 : 2 = 703
( 1 + 2017) x 2017 : 2 = 2035153
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\(\dfrac{9+x}{13-x}=\dfrac{5}{6}\\ \Rightarrow5\left(13-x\right)=6\left(9+x\right)\\ \Rightarrow65-5x=54+6x\\ \Rightarrow6x+5x=65-54\\ \Rightarrow11x=11\\ \Rightarrow x=1\)
Vậy x = 1
ĐKXĐ: \(x\ne13\)
\(\dfrac{9+x}{13-x}=\dfrac{5}{6}\)
\(\Leftrightarrow\dfrac{6\left(9+x\right)}{6\left(13-x\right)}=\dfrac{5\left(13-x\right)}{6\left(13-x\right)}\)
\(\Rightarrow6\left(9+x\right)=5\left(13-x\right)\)
\(\Leftrightarrow54+6x=65-5x\)
\(\Leftrightarrow6x+5x=65-54\)
\(\Leftrightarrow11x=11\)
\(\Leftrightarrow x=1\) (thỏa mãn ĐKXĐ)
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( x + 1 ) + ( x + 3 ) + ( x + 5 ) + ( x + 7 ) + ( x + 9 ) + ( x + 11 ) + ( x + 13 ) = 119
( x + x + x + x + x + x + x ) + ( 1 + 3 + 5 + 7 + 9 + 11 + 13 ) = 119
7x + 49 = 119
7x = 119 - 49
7x = 70
x = 70 : 7
x = 10
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\(9+\frac{x}{13}-x=\frac{5}{6}\)
\(\Leftrightarrow\frac{x}{13}-x=\frac{5}{6}-9\)
\(\Leftrightarrow x\left(\frac{1}{13}-1\right)=\frac{5}{6}-\frac{54}{6}\)
\(\Leftrightarrow\frac{-12}{13}x=\frac{-50}{6}\)
\(\Leftrightarrow x=\frac{-50}{6}\div\frac{-12}{13}\)
\(\Leftrightarrow x=\frac{50}{6}\times\frac{13}{12}\)
\(\Leftrightarrow x=\frac{650}{72}=\frac{325}{36}\)
\(9+\frac{x}{13}-x=\frac{5}{6}\)
\(\Rightarrow9+\frac{x}{13}-\frac{13x}{13}=\frac{5}{6}\)
\(\Rightarrow9+\frac{x-13x}{13}=\frac{5}{6}\)
\(\Rightarrow\frac{x-13x}{13}=\frac{5}{6}-9\)
\(\Rightarrow\frac{x-13x}{13}=-\frac{49}{6}\)
\(\Rightarrow x-13x=-\frac{49}{6}\cdot13=-\frac{637}{6}\)
\(\Rightarrow-12x=-\frac{637}{6}\)
\(\Rightarrow x=-\frac{637}{6}:(-12)=\frac{637}{72}\)
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\(\frac{9+x}{13-x}=\frac{5}{6}\)
\(\Leftrightarrow6\left(9+x\right)=5\left(13-x\right)\)
\(\Leftrightarrow54+6x=65-5x\)
\(\Leftrightarrow54-65=-5x-6x\)
\(\Leftrightarrow-11=-11x\)
\(\Leftrightarrow x=\frac{11}{11}\)
\(\Leftrightarrow x=1\)
\(\frac{9+x}{13-x}=\frac{5}{6}\)
\(\Rightarrow\text{ }6\left(9+x\right)=5\left(13-x\right)\)
\(\Rightarrow\text{ }54+6x=65-5x\)
\(\Rightarrow\text{ }54-65=-5x-6x\)
\(\Rightarrow\text{ }-11=-11x\)
\(\Rightarrow\text{ }x=-11\text{ : }\left(-11\right)\)
\(\Rightarrow\text{ }x=1\)
Số số hạng là \(\dfrac{37-5}{4}+1=\dfrac{32}{4}+1=9\left(số\right)\)
\(x\cdot5+x\cdot9+...+x\cdot37=945\)
=>\(x\left(5+9+13+...+37\right)=945\)
=>\(x\cdot\dfrac{\left(37+5\right)\cdot9}{2}=945\)
=>\(x\cdot21\cdot9=945\)
=>\(x=\dfrac{945}{189}=5\)
Tớ cảm ơn