Klas van 2023 e^i*pi+1=0 a^2+b^2=c^2 cos^2x+sin^2x=0 |a b c d|=ad-bc y-y1=m(x-x1) i^2=-1 oneindig limiet differentiaal integraal 2k+1 sn=u1+u2+...+un alpha theta sigma pi euler 3.1415926535... e=2.7182818284... 1.4142... Neutraal element sqrt{(x2-x1)^2+(y2-y1)^2}