Answer:
General solution is
[tex]x = n \pi + \frac{\pi }{8}[/tex]
Step-by-step explanation:
Step(i):-
Given cos x - sin x = √2 cos (3 x)
Dividing '√2' on both sides , we get
[tex]\frac{1}{\sqrt{2} } cos (x) - \frac{1}{\sqrt{2} } sin (x) = \frac{\sqrt{2} cos (3 x)}{\sqrt{2} }[/tex]
we will use trigonometry formulas
a) Cos ( A + B) = Cos A Cos B - sin A sin B
b) [tex]cos \frac{\pi }{4} = \frac{1}{\sqrt{2} }[/tex]
Step(ii):-
[tex]\frac{1}{\sqrt{2} } cos (x) - \frac{1}{\sqrt{2} } sin (x) = \frac{\sqrt{2} cos (3 x)}{\sqrt{2} }[/tex]
[tex]cos (\frac{\pi }{4} ) cos x - sin(\frac{\pi }{4} ) sin x = cos 3x[/tex]
[tex]cos (\frac{\pi }{4}+x ) = cos 3 x[/tex]
Step(iii):-
General solution of cos x = cos ∝ is x = 2 nπ+∝
we have [tex]cos (\frac{\pi }{4}+x ) = cos 3 x[/tex]
The general solution of [tex]cos (\frac{\pi }{4}+x ) = cos 3 x[/tex] is
⇒ [tex]3 x = 2 n \pi + (\frac{\pi }{4}+x )[/tex]
⇒ [tex]3 x- x = 2 n \pi + \frac{\pi }{4}[/tex]
[tex]2x = 2 n \pi + \frac{\pi }{4}[/tex]
final answer:-
General solution is
[tex]x = n \pi + \frac{\pi }{8}[/tex]
