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?

Question

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?

anonymous · Answer

$$(8^{2}+B^{2}+2*8*B*Cos40)=20^{2}$$

Can you proceed from here finding the value of B?

vincent-lyon.fr · Answer

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

anonymous · Answer

@rs32623 which formula are u using?

vincent-lyon.fr · Answer

He is using the Law of cosines I mentioned above.

anonymous · Answer

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)

anonymous · Answer

i think the preferred solution is Resultant = $$sqrt{A^2 + B^2}$$

vincent-lyon.fr · Answer

But this is true if and only if vectors A and B are at right angles.

anonymous · Answer

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

vincent-lyon.fr · Answer

You should end up with B = 13.20