Example 1.1.7 (a): Simple Complex Numbers |
Find the additive and multiplicative identities in C |
The additive identity is easily found to be (0, 0). As for the multiplicative identity: we are looking for the complex number (u,v) that does not change anything under multiplication, i.e. for which:
(x,y)*(u,v)=(x,y)
for all (x,y). According to the definition of multiplication:
(x,y)*(u,v) = (xu - yv, xv+yu) = (x,y)
According to the definition of equality this results in a system of two equations:
(1) xu - yv = x
(2) xv + yu = y
Multiplying the first equation by y, the second by x gives:
xyu - y2v = xy
x2v + xyu = xy
Now we subtract the equations to get:
v(x2+y2) = 0
Since this has to be true for all real x,y we have that v=0. Substituting that in equation (1) gives u=1. Therefore, the multiplicative identity is:
(1, 0)