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woleraymond
The resultant of vectors A and B has a magnitude of 20units. A has a magnitude of 8units and the angle between A and B is 40 degrees. calculate the magnitude of B?
\[(8^{2}+B^{2}+2*8*B*Cos40)=20^{2}\] Can you proceed from here finding the value of B?
Use ruler and compass. You will get the value you need, then use geometry. Either resolve your vectors or work out magnitude directly using following link: http://en.wikipedia.org/wiki/Law_of_cosines
@rs32623 which formula are u using?
He is using the Law of cosines I mentioned above.
i am using the formula for the resultant of two vectors A & B having magnitude A & B & angle between them if theta then the resultant is R=sqrt(A^2+B^2+2*A*B*Costheta)
i think the preferred solution is Resultant = \[sqrt{A^2 + B^2}\]
But this is true if and only if vectors A and B are at right angles.
if it is cosine rule then it should be R=sqrt(A^2+B^2-2*A*B*Costheta)....do you guys agree....@Vincent-Lyon.Fr @rs32623
You should end up with B = 13.20