Question

математика 5 класс помогите пожалуйста!

Answer 1

1)1/4-1/9=9/36-4/36=5/36
2)1/7-1/21=3/21-1/21=2/21
3)4/5-5/10-2/13=104/130-65/130-20/130=19/130

Answer 2

$1) \frac{1}{4} - \frac{1}{9} = \frac{1*9}{4*9} - \frac{1*4}{9*4} = \frac{9}{36} - \frac{4}{36} = \frac{5}{36} \\ \\ 2) \frac{1}{7} - \frac{1}{21} = \frac{3*1}{3*7} - \frac{1}{21} = \frac{3}{21} - \frac{1}{21} = \frac{2}{21} \\ \\ 3) \frac{4}{5} - \frac{5}{10} - \frac{2}{13} = \frac{4*26}{5*26} - \frac{5*13}{10*13} - \frac{2*10}{13*10} = \\ \\ = \frac{104}{130} - \frac{65}{130} - \frac{20}{130} = \frac{19}{130}$