kingjewel1 Posted June 26, 2005 Share Posted June 26, 2005 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. Link to comment Share on other sites More sharing options...
DQW Posted June 27, 2005 Share Posted June 27, 2005 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. Link to comment Share on other sites More sharing options...
kingjewel1 Posted June 27, 2005 Author Share Posted June 27, 2005 Cheers i've just seen the light! Thanks very much. Link to comment Share on other sites More sharing options...
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