Question
Sat September 01, 2012 By:
 

if A+B+C=180 then find the value of secA(cosBcosC-sinBsinC)

Expert Reply
Sun September 02, 2012

A + B + C = 180°.

Now, sec A (cos B.cos C - sin B.sin C)

= sec A.cos (B + C)

= sec A. cos (180° - A)

= sec A. (-cos A)

= -1
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