Two equal forces have the square of their resultant equal to three times their product. Find the angle between them.

(Ans= 60 degree)

Please help! :O

If F1 and F2 are the forces acting at a point at an angle between them, their resultant is given by

F =( F1^2 + F2^2 + 2F1F2 cos of the angle)^1/2

Hence F^2= 2F^2+2F^2Cosx= 2F^2( 1-cosx)

Therefore 1-cosx= i/2

And cosx = 1/2
Therefore x= 60 degrees

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