Inscribed angle "V" and whose sides pass through points "A" and "B". Draw line "OA". Angle "BOA" is a central angle; call it "θ". Lines "OV" and "OA" are both radii of the circle, so they have equal lengths. Therefore, triangle "VOA" is isosceles, so angle "BVA" (the inscribed angle) and angle "VAO" are equal; let each of them be denoted as "ψ". Angles "BOA" and "AOV" are supplementary. They add up to 180°, since line "VB" passing through "O" is a straight line. Therefore, angle "AOV" measures 180° − "θ". It is known that the three angles of a triangle add
Straight razor as heavy stropping and honing. Shaving is done with the blade at approximately an angle of thirty degrees to the skin and in a direction perpendicular to the edge; an incision requires the movement of the blade to be sideways or in a direction parallel to the edge. These circumstances are always avoided by the shaver, who always shaves in a direction perpendicular to the cutting edge of the blade. To be most effective, a straight razor must be kept extremely sharp. The edge is delicate, and inexpert use may bend or fold over the razor's edge. To unfold and