Question

if z1 = a + ib and z2 = c + id are two complex numbers then the product of z1z2 is defined as
1. ac + bd
2. ac + i(bd)
3.(ac - bd) + I (ad + bc)
4. none of these​

Answer 1

(a+ib)(c+id)

ac+i(ad+bc)+i^2bd

{ac+i(ad+bc)+(-1)bd} since i^2= -1

{ac+i(ad+bc)-bd}

(ac-bd)+i(ad+bc)

Answer 2

if z1 = a + ib and z2 = c + id are two complex numbers then the product of z1z2 is defined as

1. ac + bd

2. ac + i(bd)

3.(ac - bd) + I (ad + bc)

4. none of these