Find the absolute minimum and absolute maximum values of f on the given interval.

f(t) = 3t + 3 cot(t/2),

[π/4, 7π/4]

Hey guys, I'm stuck on this and on my last attempt, please help me out here,

so the derivative is -3/2cos(t)csc^2(t/2)

Then I make it = 0, etc,etc.

My answers I got were pi/2, 3pi/2 but they were both wrong. Please help me out here, PLEASE!