tìm x
x+13=15
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\(x+\left(13-15\right)=5+\left(10-7\right)\)
\(< =>x-2=8=>x=10\)
Ta có: \(x+\left(13-15\right)=5+10-7\)
\(\Leftrightarrow x-2=15-7=8\)
hay x=10
\(a,\Rightarrow x=\dfrac{7}{3}+\dfrac{6}{7}=\dfrac{49+18}{21}=\dfrac{67}{21}\\ b,\Rightarrow x=\dfrac{15}{7}-\dfrac{13}{14}=\dfrac{30-13}{14}=\dfrac{17}{14}\\ c,\Rightarrow3x=\dfrac{9}{4}-\dfrac{5}{6}=\dfrac{27-10}{12}=\dfrac{17}{12}\\ \Rightarrow x=\dfrac{17}{12}\cdot\dfrac{1}{3}=\dfrac{17}{36}\)
Bài 1:
Ta có: \(x-35\%\cdot x=\dfrac{1}{25}\)
\(\Leftrightarrow65\%\cdot x=\dfrac{1}{25}\)
\(\Leftrightarrow x=\dfrac{1}{25}:\dfrac{13}{20}=\dfrac{1}{25}\cdot\dfrac{20}{13}=\dfrac{4}{65}\)
Vậy: \(x=\dfrac{4}{65}\)
Bài 2:
a) Ta có: \(17\dfrac{2}{31}-\left(\dfrac{15}{17}+6\dfrac{2}{31}\right)\)
\(=17\dfrac{2}{31}-\dfrac{15}{17}-6\dfrac{2}{31}\)
\(=11+\dfrac{2}{31}-\dfrac{15}{17}\)
\(=\dfrac{5366}{527}\)
Ta có : A=20/11×13 + 20/13×15 +20/15×17+...+20/53×55
A = 10 ×( 2/11×13+2/13×15+...12/53×55)
A = 10 ×(1/11-1/13+1/13-1/15+1/15-1/17+...+1/53-1/55)
A = 10 × (1/11-1/55)
A =10 × 4/55
A = 8/11
\(\dfrac{x}{12}=x+\dfrac{15}{16}\)
\(\Leftrightarrow\dfrac{x}{12}=\dfrac{16x+15}{16}\)
\(\Rightarrow12\left(16x+15\right)=16x\)
\(\Leftrightarrow192x+180=16x\)
\(\Leftrightarrow176x=-180\)
\(\Leftrightarrow x=-\dfrac{45}{44}\)
Vậy \(x=-\dfrac{45}{44}\)
\(\dfrac{x}{12}=\dfrac{x+15}{16}\)
\(\Rightarrow12\left(x+15\right)=16x\)
\(\Leftrightarrow12x+180=16x\)
\(\Leftrightarrow4x=180\)
\(\Leftrightarrow x=45\)
Vậy x = 45
\(x=\dfrac{15}{13}+\dfrac{11}{13}=\dfrac{15+11}{13}=\dfrac{26}{13}\)
x= 15-13
x=2
x+13=15
x = 15 - 13
x = 2
=> Vậy x = 2
~ Ủng HỘ Mk Nha ~