En medicina se usa un isótopo de yodo para diagnosticar ciertos desórdenes de la glándulas tiroides. Para este particular isótopo radiactivo de yodo, la masa que permanece después de t horas, M(t), decrece según la fórmula: M(t) = M02-t/13.2, donde M0 es la masa inicial. ¿Cuántas horas pasarán hasta que una muestra inicial de M0 gramos de este isótopo se reduzca a la mitad?

On traditional maps, earth is represented in a flat plane, or by euclidean geometry. however, a globe is a more accurate model that comes from elliptical geometry. how does a globe represent the fact that there are no parallel lines in elliptical geometry? the equator is not parallel to any other latitudinal lines. the north and south poles are never connected by a geodesic. the geodesics connecting the north and south poles never intersect. the geodesics connecting the north and south poles intersect at both of the poles.