Originally Posted by

**MJ320** Hi everyone... new to the forum but I've read posts before that have helped me out a lot.

A patrol car is parked 50' from a long warehouse. The revolving light on top of the car turns at a rate of 30 revolutions per minute. Write theta as a function of x. How fast is the light beam moving along the wall when the beam makes an angle of theta = 45 degrees with the line perpendicular from the light to the wall.

I'm kind of lost as to where to even start here. I know I'm looking for *dx/dt*.

do I start by saying tan(theta) = x/50

theta = [arctan](x/50)

then differentiate that *dtheta/dt (which is 30) *= *d/dx *[arctan](x/50)

*u* = (x/50) so *u'* = 1/50

30 = (1/50)/[1+(x/50)^2]

Trying to see if I'm on the right path here, and if so, what is the next step. Any help would be greatly appreciated.

Thanks,

MJ