1. The problem statement, all variables and given/known data On how steep an incline(in degrees) can a car be parked without sliding down if the coefficient of static friction between the tires and the road is 0.8? 2. Relevant equations F=ma 3. The attempt at a solution My physics teacher showed how to find the acceleration for an object on an incline. He got the equation a=gsin(theta)-(mu)gcos(theta) (Sorry, I can't seem to find the sybmols for mu and theta on LaTex. I understand how he got the equation. It makes perfect sense. However, I'm having a hard time transforming the equation to get the angle of inclination. Adding mgcos(theta) to both sides yields (mu)gcos(theta)+a=gsin(theta). I would think that the acceleration is negligible since it's not moving, and I think the g's cancel out, correct? But this equation just gives 0.8cos(theta)=sin(theta). But where do I go from here? I don't know cos(theta), sin(theta), or theta. I've been looking at the theta as part of separate terms, but if they canceled out, then it would just be 0.8cos=sin. I tried the inverse of this on a hunch and got sin=36.9 degrees. This seems pretty reasonable, is this my answer? If so, why is it my answer? Thanks so much!