Step-by-step explanation:
[tex](a + b) + c \\ = \bigg(- \frac{1}{2} + \frac{3}{4} \bigg ) + \frac{5}{7} \\ = \bigg(- \frac{2}{4} + \frac{3}{4} \bigg ) + \frac{5}{7} \\ = \frac{1}{4} + \frac{5}{7} \\ = \frac{7 + 20}{28} \\ \red{ \bold{\therefore \: (a + b) + c= \frac{28}{28}}}...(1) \\ \\ a + (b + c) \\ = - \frac{1}{2} + \bigg( \frac{3}{4} + \frac{5}{7} \bigg) \\ = - \frac{1}{2} + \bigg( \frac{21 + 20}{28} \bigg) \\ = - \frac{1}{2} + \frac{41}{28} \\ = \frac{ - 14 + 41}{28} \\ \red{ \bold{a + (b + c) = \frac{ 27}{28}}}....(2) \\ \\ from \: equations \: (1) \: and \: (2) \: it \: is \\ obvious \: that: \\ \: \: \: \purple{ \boxed{\bold{ (a + b )+ c = a + (b + c) }}} \\ \: \: \: hence \: verified.[/tex]
