Inscribed angle its intersection points equals half of the central angle subtended by the chord. See also Tangent lines to circles. The inscribed angle theorem is used in many proofs of elementary Euclidean geometry of the plane. A special case of the theorem is Thales' theorem, which states that the angle subtended by a diameter is always 90°, i.e., a right angle. As a consequence of the theorem, opposite angles of cyclic quadrilaterals sum to 180°; conversely, any quadrilateral for which this is true can be inscribed in a circle. As another example, the inscribed angle theorem is the basis for several
How Are We to Live? How Are We to Live? How Are We to Live?: Ethics in an Age of Self-Interest is a book on applied ethics by bioethical philosopher Peter Singer. It was first published in 1993, with subsequent editions in later years. Singer argues that doing the right thing involves attending to the sufferings and preferences of other sentient beings. Singer presents a history of ethical thought, and attempts to refute the popular idea that humans are genetically driven to be selfish. He explains how this idea has been attributed to Thomas Hobbes and Adam Smith, and how politicians like Margaret Thatcher and