Tangentis perpendicularto the radiusTangentis perpendicularto the radiusBoth equal
VerticalanglessimilaritypostulateTherefore,Usingthe PythagoreanTheoremon Usingthe PythagoreanTheoremonThe distancebetweenthe centersof the circlesisTwo circlesaretangentto eachotherif they haveonly one commonpoint.Two circlesthat havetwo common
pointsare said tointersecteachother.
Two circlescan beexternallytangentif the circlesare situatedoutsideone anotherandinternallytangent
if one of themis situatedinsidethe other.