Is this equation correct !? Or I should use other one!?

I've got several WA on this problem. Could somebody tell me

if I should use this equation to count :

angle = acos(cos(as)*cos(bs)*cos(ai)*cos(bi)+cos(as)*sin(bs)

*cos(ai)*sin(bi)+sin(as)*sin(ai));

where as,bs are altitude and longitude of ship, and ai,bi

of iceberg ???

And could I use this:

ang2 = [ ( (secs/60)+mins )/60 + hrs ] * PI/180

to get the radian angle from given coordinates (hh^mm'ss'')

Please help!??!

Re: Is this equation correct !? Or I should use other one!?

My answer:

6875*asin(sqrt((1-cos(x)*cos(a)*cos(y-b)-sin(x)*sin(a))/2))

x,y are the ship's coordinates, and a,b are the iceberg's.

Re: Is this equation correct !? Or I should use other one!?

i think it's right ,but my sample ans is 52.14

WHY?????????????