restart;
x:=-5/sqrt(5^2+17^2);
y:=-17/sqrt(5^2+17^2);
L:=sqrt(x^2+y^2);
alpha:=arctan(y/x)+Pi;
evalf(alpha);
cos(alpha);
sin(alpha);
alpha2:=arctan(y,x);
evalc(log(x+I*y));