Why Power in a circuit is Zero (0), in which Current and Voltage are 90 Degree out of phase?

If Current and Voltage are 90 Degree Out of Phase, Then The Power (P) will be zero. The reason is that, 
We know that Power in AC Circuit 
P= V I Cos φ
if angle between current and Voltage are 90 ( φ = 90) Degree. then
Power P = V I Cos ( 90) = 0
[ Note that Cos (90) = 0] 
So if you put Cos 90 = 0→Then Power will be Zero (In pure Inductive circuit)