# Differential Equation

I am having trouble Differentiating the following with respect to ∅. Can you show me the steps I need to take to get the given correct answer please.

z = ((A+B)/2) + ((A-B)/2)Cos2∅ + C Sin2∅

Tan2∅ = (2C)/(A-B)

differentiating: dz/d(theta)=0-(A-B)sin(2∅)+2Ccos(2∅)
if dz/d∅=0, then divide by cos(2∅) on both sides and you'l get

0=-(A-B)tan(2∅)+2C

solve for tan and you'll get tan(2∅)=(2C)/(A-B)

Thanks Physeven
can you explain to me in more detail how you got the line
please. Its the actual process of differentiation I am having trouble with.

dz/d(theta)=0-(A-B)sin(2∅)+2Ccos(2∅)