Question

Prove that:

4 cosA cos(60-A) cos(60A) = cos3A

Answer 1

Hey mate!!!

cos(A-B)cos(A+B) = cos2B- sin2A ==> L.H.S = 4cosA (cos2A - sin260) ==> 4cosA (cos2A - 3/4)

==>4cos3A -3cosA = cos3A =R.H.S .Hence proved

HOPE IT HELPS.

Answer 2

Hello Friend...❤️❤️

The answer of u r question is..✌️✌️

$4cos \: a \: cos(60 - a)(cos60a) = cos3a$
Ans:✍️✍️✍️✍️✍️✍️✍️✍️✍️✍️✍️✍️


$cos(a - b)cos(a + b) = cos2b - sin2a$


$lhs = 4cosa (\: cos2a - \: sin260)$


$= 4cosa(cos2a - \frac{3}{4} )$

$= 4cos3a - 3cosa = cos3a$



Thank you..⭐️⭐️