The first thing to do is to put all the numbers you know into cells, i.e. things like omega1, omega2, m1, m2, etc. But looking at your image, the first two lines define theta1' and theta2' whereas the rest of the formulae use just theta1 and theta2. Are they meant to be the same thing or are the ones without the dashes just the old values and the ones with the dashes the new ones?
Anyway, once you've clarified that issue, you need to decide whether your angles are measured in degrees or radians - and label your Excel cells accordingly (so you don't forget
). Then, when you use the cos() and sin() functions, just make sure you're using the right units, i.e. degrees or radians. If necessary do the conversion using something like "=cos(radians(theta1))" where theta1 is the cell reference containing the value of theta1. (Incidentally, I'm still using Excel 2003 and the Help file entry for COS() contains a silly typo which might confuse you. I don't know whether that error has been corrected in later versions. You'd think MS would get such things right.