Find the value of following expression:
i30 + i80 + i120
i30 + i80 + i120 = i(28 + 2) + i80 + i120
= (i4)7 × i2 + (i4)20 + (i4)30
= – 1 + 1 + 1 = 1
[since i4 = 1, i2 = – 1]
i30 + i80 + i120 = 1