A (5j+5k), B(3i+2j-k)

[math]r=5j+5k+t(3i-3j-6k)[/math]

C is perp to r

so [math]C is (5i+5j)[/math]

O,A,B,D form the vertices of a parallelogram OBAD

Find position vector D. How do i do this one?

 

Cheers. As you can see, i've got my exam tuesday morning.

I'd appreciate it if you could give me a hand.

Thank you.

O=(0,0,0), A=(0,5,5), B=(3,2,-1)

OBAD is a parallelogram; find D.

 

As always, start from definitions - in this case, the definition of a parallelogram (and draw a picture and label it). The requirements to be met by D are :

 

(i) OD = AB

(ii) AD = OB

(iii) O,A,B,D are coplanar (ie : (OD X OB) X (OB X OA) = 0)

 

You have 3 equations in 3 unknowns. You can thus solve for them.

Cheers i've just seen the light!

Thanks very much.