Question

Tìm x biết 

a. x-8/9 =1/3

b.-4/5-8/15=-1/3-x

c.x+4/5.9+4/9.13+......+4/41.45=-37/45

Answer 1

a, \(x-\frac{8}{9}=\frac{1}{3}\)

\(\Leftrightarrow x=\frac{1}{3}+\frac{8}{9}\)

\(\Leftrightarrow x=\frac{11}{9}\)

b, \(\frac{-4}{5}-\frac{8}{15}=\frac{-1}{3}-x\)

\(\Leftrightarrow\frac{-4}{3}=\frac{-1}{3}-x\)

\(\Leftrightarrow x=1\)

Answer 2

c, \(x+\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}=\frac{-37}{45}\)

Đặt \(A=\frac{4}{5.9}+\frac{4}{9.13}+...+\frac{4}{41.45}\)

\(A=\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+...+\frac{1}{41}-\frac{1}{45}\)

\(A=\frac{1}{5}-\frac{1}{45}=\frac{8}{45}\)

Thay A vào phép tính

\(\Rightarrow x+\frac{8}{45}=\frac{-37}{45}\)

\(\Rightarrow x=-1\)