math question help?
The function f(t) = 5 cos(pi over 4t) + 11 represents the tide in Dark Sea. It has a maximum of 16 feet when time (t) is 0 and a minimum of 6 feet. The sea repeats this cycle every 8 hours. After six hours, how high is the tide?
11 feet
6 feet
8.5 feet
10.5 feet
I think its 6 feet, am I right?

Question

math question help? 
The function f(t) = 5 cos(pi over 4t) + 11 represents the tide in Dark Sea. It has a maximum of 16 feet when time (t) is 0 and a minimum of 6 feet. The sea repeats this cycle every 8 hours. After six hours, how high is the tide?
11 feet
6 feet 
8.5 feet
10.5 feet
I think its 6 feet, am I right?

alekos · Answer

If you substitute t=6 hrs what do you get?

anonymous · Answer

-2?

anonymous · Answer

or =5.215?

alekos · Answer

no way. what's cos(π/4)t when t = 6?

anonymous · Answer

sqrt2/2 ?

alekos · Answer

no, no.  it becomes cos(6π/4) 
which is?

anonymous · Answer

o?

alekos · Answer

that's right so what's the final answer in feet?

anonymous · Answer

so it is 6? @alekos

alekos · Answer

what's 5cos(3π/2) + 11 ?

remember that cos(6π/4) = cos(3π/2) = 0