1. The problem statement, all variables and given/known data Find the Arc Length from (0,3) clockwise to (2,sqrt(5)) along the circle defined by x2 + y2 = 9 2. Relevant equations Arc Length formula for integrals 3. The attempt at a solution I have the correct answer at 3arcsin(2/3), but I tried to do this without calculus the first time using the formula s = (r2θ)/2 but I seem to have lost what I once knew from geometry. I used the vectors u = <0,3> and v = <2,sqrt(5)> by the points I was given and the origin (0,0) I used the formula cos(θ) = ( u . v )/ ( ||u|| ||v||) the . here denotes the dot product. Solving for theta I have θ=cos-1(u.v)/(||u|| ||v||) and I somehow ended up with an answer roughly 90 times as large. I know it's something frustratingly basic I've mis-remembered or screwed up here. But i'm not sure what it is. Thanks in advance.