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Motion In A Plane

Question
CBSEENPH11018348

Show that if two adjacent sides of a triangle represent the two vectors, then area of the triangle is equal to half of the magnitude of the cross product of two vectors.

Solution

Let PQR be triangle formed by vectors straight A with rightwards arrow on top space and space straight B with rightwards arrow on top shown in figure.
                 
                     
From figure, the area of increment PQR is,
          straight S equals 1 half PQ. RN
space space equals 1 half PQ. PR space sinθ
          space space equals 1 half ABsinθ
space equals space 1 half open vertical bar straight A with rightwards arrow on top cross times straight B with rightwards arrow on top close vertical bar