Question

if A=60°,B=30° then prove that cos (A+B)=cosA×cosB-sinA×sinB

Answer 1

cos 90=1-1
cos 90=0
LHS=RHS

Answer 2

Hey freind
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The correct answer is:
A = 60 and B = 30

LHS

Sin (A+B) / cos A cos B

Put the values of A and B

= Sin(60+30) / cos 60 * cos 30

= Sin 90 / cos 60 * cos 30

= 1/ (1/2)*(√3/2)

= 1/ (√3/4)

= 4/√3

Now,

RHS

Tan A + Tan B

Put the values of A and B

= Tan 60 + Tan 30

= √3 + 1/√3

= (3+1)/√3

= 4/√3

Here, LHS = RHS

So, sin (A+B)/cos A cos B = Tan A + Tan B (pvd)
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Hope this helps u

By jerman