cos (A+B). cos (A-B)=?
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Answer:
Hy
Step-by-step explanation:
Therefore,
LHS=cos(a+b)cos(a−b)
=(cosacosb−sinasinb)(cosa cosb + sina sinb)
=cos²a cos² b − sin² a sin²b
=cos² b(1 − sin²a)−sin² a(1 − cos²b)
=cos²b−cos²bsin²a−sin²a + cos²bsin²a
= cos²b - sin²a
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