Ancient Indian mathmatician aryabhatta is credited as inventor of trignometry.
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Guido d'Arezzo
Complement of a given angle = (90 - given angle) Supplement of a given angle = (180 - given angle)
Measure it or use trigonometry if the 'included' angle is given.
The answer depends on what you need to do. You can always use a ruler to measure the sides. Or you may be able to use trigonometry to calculate them - except that you will still need to know the length of one side.
With Pythagoras' theorem or trigonometry depending on the information you are given.