Question

1.so sánh các phân số sau bằng cách nhanh nhất

a)\(\frac{19}{24}và\frac{34}{39}\) b)\(\frac{1}{3};\frac{3}{5}và\frac{5}{7}\) c)\(\frac{a+1}{a+2}và\frac{a+2}{a+3}\)

Answer 1

Lời giải:

a) \(\frac{19}{24}=1-\frac{5}{24}; \frac{34}{39}=1-\frac{5}{39}\)

Mà \(\frac{5}{24}> \frac{5}{39}\Rightarrow 1-\frac{5}{24}< 1-\frac{5}{39}\)

\(\Rightarrow \frac{19}{24}< \frac{34}{39}\)

b)

\(\frac{1}{3}=\frac{3}{9}< \frac{3}{5}\)

\(\frac{3}{5}=\frac{15}{25}< \frac{15}{21}=\frac{5}{7}\)

\(\Rightarrow \frac{1}{3}< \frac{3}{5}< \frac{5}{7}\)

c)

\(\frac{a+1}{a+2}=1-\frac{1}{a+2}< 1-\frac{1}{a+3}=\frac{a+2}{a+3}\)