In triangle BCF, sides BC and BF are equal, since they are both the length s of one side of the pentagon.
angle B is 18° (90°-72°, the exterior angle of the pentagon)
So, since BCF is isosceles, angle BCF = (180-18)/2 = 81°
A REGULAR PENTAGON AND A SQUARE ABFG ARE FORMED ON OPPOSITE SIDE OF AB FIND ANGLE BCF.
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