Why Does the Derivative of 2 + tan(x/2) Include a .5 Term?

[bobsmith76]

Homework Statement

I understand everything except why the derivative of 2 + tan (x/2) is .5 + sec^2(x/2)
I don't understand the .5 part. I understand the sec part. I would think the derivative of 2 would be C, or just disappear.

 

[bobsmith76]

never mind. I got it. I've got to use the chain rule. the derivative of t/2 is 1/2