Isospin relations are used to eliminate hadronic uncertainties in various CP asymmetries in 8 decays. In addition to the simple triangle relations for the m.m mode, we study quadrilateral relations for Km and pentagon relations for pm. A combined angular and isospin analysis is required for pp. These methods are useful also for three-body decays such as Kmm. . The magnitude of the penguin amplitude can be extracted in various modes. The theoretical principles behind this analysis can be experimentally tested through sum rules for decay rates prior to the measurement of CP asymmetries.