SOLUTION: I don't understand how to work these types of problems: Sec^2 18 degrees - tan^2 18 degrees. Thanks!

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Question 415076: I don't understand how to work these types of problems:
Sec^2 18 degrees - tan^2 18 degrees.
Thanks!
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
There is a variant of the Pythagorean identity: %28sec+x%29%5E2+=+%28tan+x%29%5E2+%2B+1. Hence %28sec+18%5Eo%29%5E2+=+%28tan+18%5Eo%29%5E2+%2B+1, and so %28sec+18%5Eo%29%5E2+-+%28tan+18%5Eo%29%5E2+=+1