Question

Tìm x biết:\(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+....\frac{1}{\chi\left(\chi+1\right):2}=\frac{2013}{2015}\)

Answer 1

\(\frac{2}{6}+\frac{2}{12}+...+\frac{2}{x\left(x+1\right)}=\frac{2013}{2015}\)

\(2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{x\left(x+1\right)}\right)=\frac{2013}{2015}\)

\(2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{x}-\frac{1}{x+1}\right)=\frac{2013}{2015}\)

\(2\left(\frac{1}{2}-\frac{1}{x+1}\right)=\frac{2013}{2015}\)

\(\frac{1}{2}-\frac{1}{x+1}=\frac{2013}{2015}:2\)

\(\frac{1}{x+1}=\frac{1}{2}-\frac{2013}{4030}\)

\(\frac{1}{x+1}=\frac{1}{2015}\)

=>x+1=2015

=>x=2014

Answer 2

=2014 k mk đi

Answer 3

\(x=2014\)

Answer 4

x=2014

k minh minh k lai cho

Answer 5

đáp số:x=2014

ai k mk mk sẽ k lại ( nhớ k mk nha mk thank nhiều)^^