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.