Question

cos (a+b) x cos (a-b)=​

Answer 1

Step-by-step explanation:

cos (a+b) x cos (a-b)=

[cos (a) cos(b) - sin(a) sin(b)] × [cos a cos(b) + sin(a) sin(b) ]

Note:-

(a +b)×(a-b) = a^2 - b^2

cos^2 (a) cos^2 (b) - sin^2 (a) sin^2 (b)