CBSE Class 11-science Answered
Prove
Asked by | 27 Aug, 2008, 09:01: PM
Expert Answer
2cosa cosb cos(a+b) = 2 cosa cosb(cosacosb - sinasinb)
=2cos2a cos2b - 2cosa cosb sina sinb
= cos2a cos2b +cos2a cos2b - 2cosa cosb sina sinb
=(1-sin2a)cos2b + (1-sin2b) cos2a - 2cosa cosb sina sinb
now L.H.S. will be
=cos2a + cos2b -(1-sin2a)cos2b - (1-sin2b) cos2a + 2cosa cosb sina sinb
=sin2a cos2b +sin2b cos2a + 2cosa cosb sina sinb
=(sina cosb+cosa+sinb)2 = sin2(a+b)
Answered by | 08 Sep, 2008, 06:00: PM
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