Question

tìm x,biết:

\(\dfrac{1}{6}x+\dfrac{1}{12}x+\dfrac{1}{20}x+...+\dfrac{1}{380}x=9\)

câu này dễ lắm trả lời đúng mình tick

Answer 1

\(\dfrac{1}{6}x+\dfrac{1}{12}x+\dfrac{1}{20}x+...+\dfrac{1}{380}=9\)

\(x\left(\dfrac{1}{6}+\dfrac{1}{12}+\dfrac{1}{20}+...+\dfrac{1}{380}\right)=9\)

\(x\left(\dfrac{1}{2.3}+\dfrac{1}{3.4}+\dfrac{1}{4.5}+...+\dfrac{1}{19.20}\right)=9\)

\(x\left(\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{19}-\dfrac{1}{20}\right)=9\)

\(x\left(\dfrac{1}{2}-\dfrac{1}{20}\right)=9\)

\(x.\dfrac{9}{20}=9\)

\(x=9:\dfrac{9}{20}\)

\(x=20\)

Vậy \(x=20\)