Answer this.....

The word lol (laughing out loud) at the last of my post is a proof to it....
and if someone felt bad over that then dosen't matters me much.......

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my question is that :

if A + B + C = 180°

Then A + B = 180° - C

=> Cos (A + B) = Cos(180° - C) = - Cos C

or, Cos (A + B) = - Cos C

Now it is valid for all values of A, B and C satisfying A + B + C = 180⁰

So, like this, is there any conversion for cos (A - B)????.... If not then fine......

i don't want 100 or 101 answers to it. I want simply 1.... if someone can...

and no lolz this time... plz...

cosA.cosB + sinAsinB

-cos(B+C).-cos(A+C) + sin(B+C)sin(A+C)

= cos(B+C).cos(A+C) + sin(B+C)sin(A+C)

Thankyou sir this is what i wanted...............