[SOLVED] FINDING RADIUS OF CURVATURE OF CARDIODE r=a(1-cost)

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 but **i 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 :- __

__ radius of curvature__ =((r^2+(r1)^2 )^3/2)/r^2+2(r1)^2-r(r2) were

r1 is first derivative of r and

**r2 is second derivative of r**

__Please any body help me this problem is driving me crazy,__

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