Option A

<em><u>Solution:</u></em>
Given that we have to rewrite with only sin x and cos x
Given is cos 3x

We know that,

Therefore,
---- eqn 1
We know that,


Substituting these values in eqn 1
-------- eqn 2
We know that,

Applying this in above eqn 2, we get



Therefore,

Option A is correct
Use elimination
Multiply first equation by 4
12a - 8b = 56
12a + 9b = 39
Subtract both
-17b = 17
b = -1
Plug in -1 for b
3a - 2(-1) = 14
3a = 12, a = 4
Final answer: a = 4, b = -1
Answer:
D as it is the obtuse
Step-by-step explanation: