IaI=IbI= 1

C2+D2 = 1； m2+n2= 1

And because vector a* vector b=- 1/2.

So cm+dn=- 1/2.

Ia+2bI= under the radical sign ((c+2m)2+(d+2n)2)

ia+2bi 2 = C2+4 m2+4cm+D2+4 N2+4dn = 3。

So Ia+2bI= root number 3

Note: The number after the letter is square.