What is the magnitude of the cross product vec{A} times vec{B}?
What is the magnitude of the cross product vec{C} times vec{D}?
3 Answers

If a vector b makes an angle θ with vector a.
The magnitude of the cross product is :
a X b = a.bsinθ
In your examples
(a) a = 6 and b = 4 θ = 180° – 135° = 45°
a X b = 6 X 4 X sin(45°) = 24(1/√2) = 12√2 units (Multiplying top and bottom be √2)
(b) In this case vectors are anti parallel so θ = 180°
c X d = 0 since sin(180°) = 0.

Magnitude Of Cross Product

http://en.wikipedia.org/wiki/Cross_product#Definit…
simple problem. why not try and post back if you get stuck. you’ll be better off down the road if you at least try…
cheers