The question reads:

With respect to the origin O, the points A,B,C,D have position vectors given by

OA= 4i + k,OB= 5i - 2j - 2k,OC= i + j,OD= -i -4k

(i) Calculate the acute angle between the lines AB and CD

Completed this, answer is theta = 99.03degrees

(ii) Prove that the lines AB and CD intersect

(iii) The point P has position vector i + 5j + 6k. Show that the perpendicular distance from P to the line AB is equal tosqrt3

(I can solve this one)

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(ii) Prove that the lines AB and CD intersect

Please could someone help me with a formula here?

Thank you kindly