A regular hexagon ABCDEF has center O. Prove [math]\bigtriangleup ABO[/math] is an equilateral.
AB is a diameter of circle O. C is a point on the circumference. Prove [math]\angle ACB=90^\circ[/math]
Quadrilateral ABCD is inscribed in a circle. Prove that [math]\angle A+\angle C=180^{\circ}[/math]
Given PA and PB are tangents to a circle from point P. Prove [math]PA\cong PB[/math].