Vector OF= 1/5 vector d+4/5 vector b.
Vector EF= 1/5 vector d- 1/4 vector a.
Vector EC= vector c- 1/4 vector a-3/4 vector b.
(2) vector ED= vector EO+ vector OD= vector d- 1/4 vector a-3/4 vector b.
Vector EF= 1/5 vector d- 1/4 vector a.
The two lines are not perpendicular.