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let a=cosA+cosb-cos(A+B) and b=4sin(A/2)...

let `a=cosA+cosb-cos(A+B)` and `b=4sin(A/2)sin(B/2)cos((A+B)/2)` Then a-b is

A

1

B

zero

C

`-1`

D

`1/2`

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The correct Answer is:
A
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