Question

If sin 3A = cos (A - 26°). where 3A is an acute angle, then the value of A is
(a) A = 13°
(b) A = 64°
(c) A = 29°
(d) A = 26°
{AMU +2 SCIENCE ENTRANCE 2013-14}

Answer 1

sin 3A = cos (A-26°)

we know that , sin theta = cos (90°-theta)

=> cos (90°-3A) = cos (A-26°)


=> 90°-3A = A-26°

=> 116° = 4A

=> 116°/4 = 29° = A


c) A = 29°

is correct Option

hope this helps

Answer 2

Hi Rehan and others .....

sin 3A = cos ( A - 26° )

cos ( 90 - 3A ) = cos ( A + 26° )

90 - 3A = A - 26

116 = 4A

A = 29°.....

Hope it helps