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Question 7. 4. Show that the area of the triangle contained between the vectors a and b is one half of the magnitude of a × b.


Consider two vectors OK=|a| and OM=|b|, inclined at an angle θ, as shown in the following figure.
In ΔOMN, we can write the relation:
sinθ=MNOM=MN|b|
MN=|b|sinθ
|a×a|=|a||b|sinθ
=OK·MN×22
=2×Area of OMK
Area of OMK=12|a×b|