If there are two vectors of magnitude a and b then their resultant magnitude is written by
(a2 + b2 + 2abcos"\\theta")1/2 where θ is the angle between the two vectors
a) when a and b are in the same direction
θ =00 and as cos00=1
then magnitude of two vectors become "\\vert a+b \\vert=" (a2+b2+2ab)1/2=
=(a+b) = |a| + |b|
b) when a and b are in the opposite direction
θ =1800 and as cos1800=-1
then magnitude of two vectors become "\\vert a-b \\vert=" (a2+b2-2ab)1/2=
=(a-b) = |a| - |b|
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