Question

sec 0=1. why? how can it be possible?

Answer 1

as cos 0=1
and we know 1/cosa=seca
so sec0=1

Answer 2

Cos x =  1 - (1/2!) x 2 + (1/4!) x 4 - (1/6!) x 6 +...- (1/n!) x n 

So Cos 0 = 1
So Cos x = 1/sec x

Sec x = 1/cos x
 
sec x = 1/1