Submitted by helpmeh on Wed, 01/11/2017 - 17:57
I need help with STEP 1 2003 - Question 3 iii.
I completed the square and found that cos(theta/2) = 1/2 - root3/2.
I have reached the stage where I have that half theta = arcos(1/2-root3/2)
From here I'm not sure how to reach end conclusion.