Evaluate (1 + i10 + i20 + i30).
we have, 1 + i10 + i20 + i30
= 1 + (i4)2.i2 + (i4)5 + (i4)7.i2
We know that, i4 = 1
⇒ 1 + (1)2.i2 + (1)5 + (1)7.i2
= 1 + i2 + 1 + i2
= 1 -1 + 1 -1
= 0