In a triangle with sides o,h, c, and angle 3, between o. and b, the following relation is satised .:';I.2+tr2 2ohm'= c"2 (of course, I] if. H :1 1T). As a corollary we have a slightlyr stronger version of Pythagoras"l Theorem: the triangle is a right triangle, with hypotenuse c, if and onl:,r if {12 + 52 = (:2. This is true, in particular, if :1 : b : c = 3 : 4 : 5 {this \"precursor\" to I\"'}rthEL1:T,ora.*-:.l Theorem has been known since the earliest recorded history]. Suppose now that b = 3.,c : 1E], and o. = io, i.e., that the length of o is known up to an error, with % = .02. What relative incertitude does this entail on our estimate of 3 a E