Приведите подобные слагаемые: А) 2/3b+19/21b; B)-2/3b-19/21b; C)-2/3b+19/21b; D)1/2a+3/5a;

Решите задачу:

$1) \frac{2}{3} b + \frac{19}{21}b = \frac{14b+19b}{21} = \frac{33b}{21} = \frac{11b}{7} \\ \\ 2) - \frac{2}{3} b - \frac{19}{21}b = \frac{-14b-19b}{21} = \frac{-33b}{21} = \frac{-11b}{7} \\ \\ 3) - \frac{2}{3} b + \frac{19}{21}b = \frac{-14b+19b}{21}} = - \frac{5b}{21} \\\\ 4) \frac{1}{2}a+\frac{3}{5}a = \frac{5a+6a}{10} = \frac{11a}{10}$