ok, so what about deriving the other ratios from knowing that sine=0.642?
I did this last year, but GUESS WHAT? I have no textbook this year and my teacher is... is... well.... no comment.
Once you know the sine of an angle, then you can get all the other functions using this famous identity:
Sin^2(x) + Cos^2(x) =1. To see how, go online to this link: https://en.wikipedia.org/wiki/Sine
Go down the page to "Other Trigonometric Functions" and look at the first column.