Derivative of a function with trig functions

[YungJoker300]

If dF/dtheta is (-mu)W(musintheta + costheta)^-2(mucostheta-sintheta) (W is the object's weight) what does theta equal when dF/dtheta is 0. And if W is 30 lbs and mu is 0.4, at what value of theta does dF/dtheta equal zero.

 

[tkhunny]

\(\displaystyle \frac{dF}{d\theta} = -\mu\cdot W\cdot\frac{\mu\cdot\cos(\theta)-\sin(\theta)}{(\mu\cdot\sin(\theta)+\cos(\theta))^{2}}\)

That?

I guess you need to find where the Numerator is zero (0) without the denominator being zero (0) at the same time. That would be relatively easy without that sticky \(\displaystyle \mu\) in there.

Let's see what you get.