Project one line into another

Hello I have two straight line and trying to project one into another. There is something wrong with my code. Any advice ?

L1     % line one ( vector )
L2     % line 2 ( vector )
ln1i   % length of point i in line one
ln2i   % length of point i in line two
m1 : slope of line one
m2 : slope of line 2
an = ((m1-m2)/(1+m1*m2));  % angle in dgree
L11= ln1i*cosd(an); % projection of line one into line 2.

I get wrong values always. Am i doing any mistake ?