I have posted a question at homework forum, nobody's answering my query. I'm now going try my luck at this forum. I'm doing a self review on spherical trigonometry and I'm now implementing Napier's Rules in solving right spherical triangles, the first problem goes like this: In a right spherical triangle (C=90 degrees), A=69 degrees and 50.8minutes, c=72 degrees and 15.4minutes, find B, a, b. Using Napier's rules, I get a=63 degrees and 23.8 minutes b= 47 degrees7.0 minutes, B=50 degrees and 17.7 minutes a note is given at the end of the question stating that "The supplementary value is not admissible since 'A' (angle A) and 'a' (side a) do not terminate at the same quadrant" - but by inspection, the two values terminate on the first quadrant. This completely confuses me, can anyone elaborate. A million thanks, PS: I'm using "PLANE AND SPHERICAL TRIGONOMETRY" By Paul Rider.