hi friend its eazy

let  be the angle between the vector A and B

then let R be the resultant

thenyou know tha if R is  to A then R.A=0

R=A+B

R.A=A^2+ABcos

A mag =Bcos

now you know that

(A+B) mag=R mag=B/2mag-----------------------mag is magnitude

take the components of A on x axis and Y axis

taking the angle with negative x axis to be 180-

and replace the value of A in(A+B) mag=R mag=B/2mag by Bcos and you will see that B cancells out you will get value of  easily

bye

plzzz rate me

 

but what is the need of taking 180-                      

        we can put value of                         A = B cos

in A+B(mag)=B/2(mag)

anyway a salute to you for helping me out