Question

if a= -8,b=-7 and c=6 verify that (a+b)+c = a+(b+c)

Answer 1

(-8+-7)+6=-8+(-7+6)
-15+6=-8+-1
-9=-9
hence, verified

Answer 2

replace
a=-8
b=-7
c=6
(-8+-7)+6 = -8+(-7+6)
(-8-7)+6 = -8+(-7+6)
(-15)+6 = -8+(-1)
-15+6 = -8 -1
-9 = -9
hence proved