Active risk squared

CFA Level II Portfolio Management
#1

Why do we use Active risk squared = active factor risk + active specific risk ?

Cant we just use active risk instead? Thanks

#2

Variances (with correlations of zero) add.

Standard deviations do not.

#3

Whats the difference between active risk and active risk squared?

#4

5% vs 5%2 = 0.25%