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(a) Prove that cos 3A = 4cos³ A - 3 cos A​
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(a) Prove that cos 3A = 4cos³ A - 3 cos A​

User Abhishek Gahlout
by
7.8k points

1 Answer

5 votes

Answer:

Explanation:

cos 3A = cos (2A+A)

= cos 2A cos A - sin 2A sin A

= (2cos
A^(2) -1) cos A - (2sinAcosA) sinA

=2cos
A^(3)-cosA - 2sin
A^(2)cosA

=2cos
A^(3)-cosA -2(1 -cos
A^(2))cosA

=2cos
A^(3) - cosA - 2 cosA+ 2cos

⇒ ∴4cos
A^(3) -3 cosA

User Trikelef
by
9.0k points
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