Question

"Question37
If A = 60° and B = 30° , verify that : cos (A +B) = cos A cos B - sin A sin B
Chapter6,T-Ratios of particular angles Exercise -6 ,Page number 289"

Answer 1

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Answer 2

Hey there! Thanka for the question!

Given,
A = 60° , B = 30°

Now,
cos (A + B) = cosA cos B - sin A sin B.

Substituting A = 60 , B = 30°

cos(90) = cos60 cos30 - sin30 sin60


We know, Trigonometry ratios of particular angles : cos90 = 0 , cos30 = √3/2 , cos60 = 1/2

0 = 1/2 ( √3/2) - (√3/2) ( 1/2)

0 = √3/4 - √3/4

Both Sides of the equation are equal.

Hence, We proved and verified that cos(A + B) = cosA cos B - sin A sin B. holds good for A = 60, B = 30°