/2*x - 2*l\ atan|---------| \ 2*a / --------------- a
atan((2*x - 2*l)/((2*a)))/a
/l - x\ -atan|-----| \ a / ------------- a
-atan((l - x)/a)/a
/l x\ -atan|- - -| \a a/ ------------- a
-atan(l/a - x/a)/a
/x - l\ atan|-----| \ a / ----------- a
atan((x - l)/a)/a