Mark the correct alternative in the following:
If A + B + C = π, then sec A (cos B cos C – sin B sin C) is equal to
B+C= 
TAKE BOTH SIDE COS
Cos (B+C)=cos(π-A)
(cos B cos C – sin B sin C) = -cos(A)
sec A (cos B cos C – sin B sin C) is equal to =-1
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