4. Find the sum of :
(a)
(b)
(c)
(d)
It is known that the sum of .
Therefore,
(a) the sum of
= 137 + (-137) + (- 217)
= - 217
(b) the sum of
= -52 + 52 = 0
(c) the sum of
= (- 231) + (81) + (39 + 192 )
= (- 81) + (- 231) + (231)
= - 81
(d) the sum of
= - (50 + 200 ) + (300)
= - 250 + (250) + 50
= 50