Question

75. Let r1 and r2 be unit vectors in the xy plane making angles a and B with the positive x-axis.
(a) Prove that r1= cos a i + sina j. r2= cos B i + sin ß i.
(b) By considering r1. r2 prove the trigonometric formulas
COS (A-B) cos a cos ß + sin a sinß,
cos (a +B)
= cos a cosß - sina sinb​

Answer 1

Answer:

Sorry, cannot do now - too much tough for me