For those of us whom have become "memory challenged" from time to time with regard to shop math, there are two shop references I would recommend which conveniently summarize the math necessary to design, as well as instructions on how to mark and layout, common geometric shapes (as well as other useful shop math and miscellany). Both are published by Popular Woodworking.
Book #1: "Practical Shop Math" by Tom Begnal, ISBN 978-1-55870-783-2, Published 2006, $14.99USD. * (Your question answered on page 170)
Book #2: "Pocket Shop Reference" by Tom Begnal, ISBN 978-1-55870-782-5, Published 2006, $14.99USD. * (Your question answered on page 47)
Another book with some useful charts, though not nearly as much so as the two above, is "Woodworker's Pocket Reference" by Charlie Self, ISBN 1-56523-239-9, Published 2005, $14.95USD.
* ISBN numbers are currently in transition from a 10-digit system to a 13-digit system. The number provided is the newer 13-digit ISBN number. If you require an equivalent older 10-digit ISBN number please subtract the first three digits (978) from the above.
I have no connections with any of these book's authors or publishers, but I have found them to be useful references from time to time and feel others might also find them to be useful. Especially those of us who don't necessarily deal with complex shapes on a day-to-day basis or have gotten a little rusty with our trigonometry.