bài1 : tìm x, biết
\(1+\frac{-x}{60}+\frac{19}{120}< \frac{x}{36}+\frac{-1}{60}< \frac{58}{90}+\frac{1}{60}\)
bài 2: C/M
1) \(\frac{1}{9}=\frac{1}{9+1}+\frac{1}{9\left(9+1\right)}\) 2) \(\frac{a}{b}=\frac{1}{m+1}+\frac{a\left(m+1\right)-b}{b\left(m+1\right)}\)
bài 3: Tính tổng các phân số có tử = 4, thỏa mãn lớn hơn \(\frac{1}{5}\)và nhỏ hơn \(\frac{1}{4}\)
Bài 2,
a, \(\frac{1}{9+1}+\frac{1}{9\left(9+1\right)}\)
\(=\frac{1}{10}+\frac{1}{9.10}\)
\(=\frac{9+1}{9.10}\)
\(=\frac{1}{9}\)
\(\Leftrightarrow\frac{1}{9}=\frac{1}{9+1}+\frac{1}{9\left(9+1\right)}\)(đpcm)
b, \(\frac{1}{m+1}+\frac{a\left(m+1\right)-b}{b\left(m+1\right)}\)
\(=\frac{b+a\left(m+1\right)-b}{b\left(m+1\right)}\)
\(=\frac{a}{b}\)
\(\Leftrightarrow\frac{a}{b}=\frac{1}{m+1}+\frac{a\left(m+1\right)-b}{b\left(m+1\right)}\)(đpcm)
