question:- r=a(1-cost)

answer :- 4/3a(sin(t/2)) (which i have to prove)

Please help me to find the radius of curvature, i know the formula everything buti have to prove the answer as :- 4/3a(sin(t/2)), which i am unable to prove it,

i cannot prove the answer as above, pls help

here is the formula for finding the radius of curvature :-

=((r^2+(r1)^2 )^3/2)/r^2+2(r1)^2-r(r2) wereradius of curvatureand

r1 is first derivative of r

r2 is second derivative of r

Please any body help me this problem is driving me crazy,