Question

[Nguyễn Trung Hiếu]

Tìm X : (\(\frac{2}{3x5}\)+ \(\frac{2}{5x7}\)+ ... + \(\frac{2}{17x19}\)) x 57 - 2 x (X - 1) = 10

Answer 1

[Minh Triều]

\(\left(\frac{2}{3\times5}+\frac{2}{5\times7}+...+\frac{2}{17\times19}\right)\times57-2\times\left(x-1\right)=10\)

\(\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{17}-\frac{1}{19}\right)\times57-2\times\left(x-1\right)=10\)

\(\left(\frac{1}{3}-\frac{1}{19}\right)\times57-2\times\left(x-1\right)=10\)

\(\frac{16}{57}\times57-2\times\left(x-1\right)=10\)

\(16-2\times\left(x-1\right)=10\)

\(2\times\left(x-1\right)=16-10\)

\(2\times\left(x-1\right)=6\)

\(x-1=6:2\)

\(x-1=3\)

\(x=3+1\)

\(x=4\)