Diagonal line of parallelogram under radical sign = BD = 2
2, vector AB = (3 3,5), vector OC = (-2,-1), then:
(AB-tOC)*OC=0
AB*OC-tOC*OC=0
[3×(-2)+5×(- 1)]-[(-2)? +(- 1)? ]t=0
t=- 1 1/5