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the angle between two vector of …

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the angle between two vector of equal magnitude is 120 degree. prove that the magnitude of their resultant is equal to either of them
  • 1 answers

Gaurav Seth 4 years, 1 month ago

Let the 2 vectors be A and B and their resultant be R.

To prove :- A=B=R.

.

For an easier way, Let us use this relation to find out theta when A=B=R.

.

R^2 = A^2 + B^2 + 2ABCostheta

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Here A^2 = B^2 = R^2 ,

Hence, R^2 = R^2 + R^2 + 2R^2 (Costheta)

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R^2 = 2R^2 + 2R^2 (Costheta)

Cos theta = (R^2 - 2R^2) / 2R^2 = (-R^2) / 2R^2

Cos theta = -1/2

Hence theta = 120 degrees.

.

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