1. The problem statement, all variables and given/known data Need help with a question ... .__." q: if the magnitude of a=2 and the magnitude of 5a-2b= 7.7, and the angles between the vectors a and b is 50 degrees determine the magnitude of b. 2. Relevant equations 3. The attempt at a solution first I drew a diagram... then i used cosine law to solve for b l5a-2bl = (5x2) + (2b)^2 -2(5x2)(2b)cos50 7.7= 10 +4b^2 -40b cos 50 this worked out to be a quadratic, the zeros i found were 6.3 & 0.09, but then i subbed those numbers back into the cosine law i don't get back 7.7... I tried this question like this, l5a-2bl = (5x2)^2 + (2b)^2 -2(5x2)(2b)cos50, but it didn't work out either. help?