# What is the derivative of sin(a/2 + d/2)/sin(a/2)?

$\frac{d}{\mathrm{dx}} \sin \frac{\frac{a}{2} + \frac{d}{2}}{\sin} \left(\frac{a}{2}\right) = 0$
Assuming that $a$ and $d$ are constants, then the entire expression is constant, thus:
$\frac{d}{\mathrm{dx}} \sin \frac{\frac{a}{2} + \frac{d}{2}}{\sin} \left(\frac{a}{2}\right) = 0$