



 
Hi Dale, What you have is an isosceles triangle and you know the lengths of the three sides. Join the vertex C to the midpoint M of the base. If the radius is r and the length of the chord is c then triangle CMB is a right triangle with BC = r and MB = c/2. Hence the sine of the angle BCM is (c/2)/r = c/(2r). Hence the central angle BCA has measure
I hope this helps,  


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