Originally Posted by
Grandad Hello magentaritaI'm not quite sure what you mean by this. Obviously you don't mean that you can't find two numbers that add together to make 100.
Do you mean how do you find $\displaystyle \cos100^o$ without using a calculator? If so, I'm not sure that you can. There are some angles - like $\displaystyle 30^o, 45^o, 60^o, 90^o$ and so on - that have easy sines and cosines, and you may not need a calculator for these. And you may be able to find two of these special angles that will combine to give $\displaystyle 100^o$ (perhaps by adding, subtracting, doubling, and so on), but I can't think of any at present.
Is this what you meant?
Grandad