cos (a+b) = 3/5 , and cos (a-b) = 4/5 then evaluate sin2a - Maths - Introduction to Trigonometry

Question

cos (a+b) = 3/5 , and cos (a-b) = 4/5 then evaluate sin2a

Anuradha Sharma · Accepted Answer

We have,cosA+B=35sinA+B = 1 - cos2A+B = 1 - 925 = 1625 = 45cosA-B=45sinA-B = 1 - cos2A-B = 1 - 1625 = 925 = 35sin 2A = sinA+B + A-B=sinA+B 
 cosA-B + cosA+B 
 sinA-B=45×45 + 35×35=1625 + 925=2525=1