+118608 8pi/2 is 2 complete revolutions so 11pi/2 is the same as 3pi/2 as far as the value of sine is concerned.
On the unit circle, 3pi/2 is the point (0,-1) DRAW it do see what i mean.
sine is given by the y value on the unit circle so sin(3pi/2)= -1
So
sin(11pi/2)= -1
I can try and explain more, maybe with a diagram, if you need me too. 
+118608 8pi/2 is 2 complete revolutions so 11pi/2 is the same as 3pi/2 as far as the value of sine is concerned.
On the unit circle, 3pi/2 is the point (0,-1) DRAW it do see what i mean.
sine is given by the y value on the unit circle so sin(3pi/2)= -1
So
sin(11pi/2)= -1
I can try and explain more, maybe with a diagram, if you need me too.
