Question

[Bùi Tuyết Sinh]

bài 1 tìm x 

a, \(\frac{1}{2}\)-(\(\frac{2}{3}\).x-\(\frac{1}{3}\))=\(\frac{2}{3}\)    b, \(\frac{3}{x+5}\)=15%

bài 2 tính hợp lý tổng sau

A=\(\frac{1}{1.2}\)+\(\frac{1}{2.3}\)+\(\frac{1}{3.4}\)+...+\(\frac{1}{49.50}\)

Answer 1

[Bùi Tuyết Sinh]

mong là trước ngày mai

Answer 2

[Yen Nhi]

`Answer:`

Bài 1:

a. \(\frac{1}{2}-\left(\frac{2}{3}x-\frac{1}{3}\right)=\frac{2}{3}\)

\(\Leftrightarrow\frac{1}{2}-\frac{2}{3}x+\frac{1}{3}=\frac{2}{3}\)

\(\Leftrightarrow\frac{5}{6}-\frac{2}{3}x=\frac{2}{3}\)

\(\Leftrightarrow-\frac{2}{3}=\frac{2}{3}-\frac{5}{6}\)

\(\Leftrightarrow-\frac{2}{3}x=-\frac{1}{6}\)

\(\Leftrightarrow x=-\frac{1}{6}:-\frac{2}{3}\)

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

b. \(\frac{3}{x+5}=15\%\left(ĐKXĐ:x\ne-5\right)\)

\(\Leftrightarrow\frac{3}{x+5}=\frac{3}{20}\)

\(\Leftrightarrow\frac{60}{20\left(x+5\right)}=\frac{3\left(x+5\right)}{20\left(x+5\right)}\)

\(\Leftrightarrow60x=3x+15\)

\(\Leftrightarrow-3x=-45\)

\(\Leftrightarrow x=15\)

Bài 2:

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}\)

\(=1-\frac{1}{50}\)

\(=\frac{49}{50}\)