Question 70

cos(A+B) + cos(A-B) is equal to ?

Solution

Expression : cos(A+B) + cos(A-B)

= $$(cosAcosB - sinAsinB) + (cosAcosB + sinAsinB)$$

= $$(cosAcosB+cosAcosB) + (sinAsinB-sinAsinB)$$

= $$2cosAcosB$$

=> Ans - (A)

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