Plz check my work

The depth of water h, is meters at the entrance to a harbour t hours after midnight can be modelled by the equation h=5+2.6cos 4*pi*t/25.
At what rate is the depth of the water changing at 10 am?

So dh/dt= -1.3069sin (4*pi*t/25)
Which is correct

Then to find depth of water change we substitute t=10 yes?
When I did I get -0.114
Which doesn't make sense??

ANSWER says:at t=10 dh/dt= 1.24m

Question

Plz check my work 

The depth of water h, is meters at the entrance to a harbour t hours after midnight can be modelled by the equation h=5+2.6cos 4*pi*t/25.
At what rate is the depth of the water changing at 10 am? 

So dh/dt= -1.3069sin (4*pi*t/25)
Which is correct 

Then to find depth of water change we substitute t=10 yes?
When I did I get -0.114 
Which doesn't make sense??

ANSWER says:at t=10 dh/dt= 1.24m

anonymous · Answer

you got the derivative right. Just did the algebra wrong when you plugged 10 in for t.

anonymous · Answer

If you used a calculator, make sure it's in radian mode

marigirl · Answer

Oh yes radian mode... how could I forget  .. lol
Thanks