MHB How Can You Solve Complex Trigonometric Equations?

AI Thread Summary
The discussion revolves around solving the complex trigonometric equation involving sine and cosine functions. Participants share their solutions and express camaraderie through light-hearted banter. One contributor acknowledges another's correct result while presenting their own similar solution. The tone remains playful, with comments reflecting a mix of frustration and humor about the complexity of the problem. Overall, the thread highlights collaborative problem-solving in trigonometry.
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Solve the equation

$$\sqrt{3}\sin x(\cos x-\sin x)+(2-\sqrt{6})\cos x+2\sin x+\sqrt{3}-2\sqrt{2}=0$$
 
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anemone said:
Solve the equation

$$\sqrt{3}\sin x(\cos x-\sin x)+(2-\sqrt{6})\cos x+2\sin x+\sqrt{3}-2\sqrt{2}=0$$
I'm beginning to think that you are a sadist...

-Dan
 
Here is my solution:

We are given to solve:

$$\sqrt{3}\sin(x)(\cos(x)-\sin(x))+(2-\sqrt{6})\cos(x)+2\sin(x)+\sqrt{3}-2\sqrt{2}=0$$

First, let's do the distribution dance...

$$\sqrt{3}\sin(x)\cos(x)-\sqrt{3}\sin^2(x)+2\cos(x)-\sqrt{6}\cos(x)+2\sin(x)+\sqrt{3}-2\sqrt{2}=0$$

Now, regroup...

$$\sqrt{3}(\sin(x)\cos(x)+1-\sin^2(x))+2(\sin(x)+\cos(x))-\sqrt{6}\cos(x)-2\sqrt{2}=0$$

Within the second factor of the first term, apply a Pythagorean identity:

$$\sqrt{3}(\sin(x)\cos(x)+\cos^2(x))+2(\sin(x)+\cos(x)-\sqrt{2}-\sqrt{6}\cos(x)=0$$

Now factor:

$$\sqrt{3}\cos(x)(\sin(x)+\cos(x))+2(\sin(x)+\cos(x)-\sqrt{2}(\sqrt{3}\cos(x)+2)=0$$

$$(\sin(x)+\cos(x))(\sqrt{3}\cos(x)+2)-\sqrt{2}(\sqrt{3}\cos(x)+2)=0$$

$$(\sin(x)+\cos(x)-\sqrt{2})(\sqrt{3}\cos(x)+2)=0$$

The second factor has no real root, hence we are left with:

$$\sin(x)+\cos(x)=\sqrt{2}$$

$$\sin\left(x+\frac{\pi}{4} \right)=1$$

$$x+\frac{\pi}{4}=\frac{\pi}{2}+2k\pi$$ where $$k\in\mathbb{Z}$$

$$x=\frac{\pi}{4}+2k\pi=\frac{\pi}{4}(8k+1)$$
 
MarkFL said:
Here is my solution:

We are given to solve:

$$\sqrt{3}\sin(x)(\cos(x)-\sin(x))+(2-\sqrt{6})\cos(x)+2\sin(x)+\sqrt{3}-2\sqrt{2}=0$$

First, let's do the distribution dance...

$$\sqrt{3}\sin(x)\cos(x)-\sqrt{3}\sin^2(x)+2\cos(x)-\sqrt{6}\cos(x)+2\sin(x)+\sqrt{3}-2\sqrt{2}=0$$

Now, regroup...

$$\sqrt{3}(\sin(x)\cos(x)+1-\sin^2(x))+2(\sin(x)+\cos(x))-\sqrt{6}\cos(x)-2\sqrt{2}=0$$

Within the second factor of the first term, apply a Pythagorean identity:

$$\sqrt{3}(\sin(x)\cos(x)+\cos^2(x))+2(\sin(x)+\cos(x)-\sqrt{2}-\sqrt{6}\cos(x)=0$$

Now factor:

$$\sqrt{3}\cos(x)(\sin(x)+\cos(x))+2(\sin(x)+\cos(x)-\sqrt{2}(\sqrt{3}\cos(x)+2)=0$$

$$(\sin(x)+\cos(x))(\sqrt{3}\cos(x)+2)-\sqrt{2}(\sqrt{3}\cos(x)+2)=0$$

$$(\sin(x)+\cos(x)-\sqrt{2})(\sqrt{3}\cos(x)+2)=0$$

The second factor has no real root, hence we are left with:

$$\sin(x)+\cos(x)=\sqrt{2}$$

$$\sin\left(x+\frac{\pi}{4} \right)=1$$

$$x+\frac{\pi}{4}=\frac{\pi}{2}+2k\pi$$ where $$k\in\mathbb{Z}$$

$$x=\frac{\pi}{4}+2k\pi=\frac{\pi}{4}(8k+1)$$

Thank you MarkFL for participating and your result is correct!:D

My solution is quite similar to yours but I figure it is only fair if I posted mine as well here...

My solution:
We're given

$$\sqrt{3}\sin(x)(\cos(x)-\sin(x))+(2-\sqrt{6})\cos(x)+2\sin(x)+\sqrt{3}-2\sqrt{2}=0$$

I noticed there is another term $$(2\sin x)$$ which I could group it to the first term, after I multiplied $$\sqrt{3}$$ onto everything inside the parentheses...

$$\sin(x)(\sqrt{3}\cos(x)-\sqrt{3}\sin(x)+2)+(\sqrt{2}\sqrt{2}-\sqrt{2}\sqrt{3})\cos(x)+\sqrt{3}-2\sqrt{2}=0$$

Also, the second term can be simplified further to get

$$\sin(x)(\sqrt{3}\cos(x)-\sqrt{3}\sin(x)+2)+\sqrt{2}\cos(x)(\sqrt{2}-\sqrt{3})+\sqrt{3}-2\sqrt{2}=0$$

And we can rewrite$$\sqrt{3}$$ as $$(\sqrt{3})(1)=\sqrt{3}\left(\sin^2(x)+\cos^2 (x) \right)=\sqrt{3}\sin^2(x)+\sqrt{3}\cos^2(x)$$ and observe that each of these two terms can be simplified out by collecting them to the first and second terms of the equation above:

$$\sin(x)(\sqrt{3}\cos(x)-\sqrt{3}\sin(x)+2)+\sqrt{2}\cos(x)(\sqrt{2}-\sqrt{3})+\sqrt{3}\sin^2(x)+\sqrt{3}\cos^2(x)-2\sqrt{2}=0$$

$$\sin(x)(\sqrt{3}\cos(x)-\sqrt{3}\sin(x)+2+\sqrt{3}\sin(x))+\sqrt{2}\cos(x)\left(\sqrt{2}-\sqrt{3}+\frac{\sqrt{3}}{\sqrt{2}}\cos^2(x) \right)-2\sqrt{2}=0$$

$$\sin(x)(\sqrt{3}\cos(x)+2)+\sqrt{2}\cos(x) \left(\frac{2-\sqrt{2}\sqrt{3}+\sqrt{3}\cos(x)}{\sqrt{2}} \right)-2\sqrt{2}=0$$

$$\sin(x)(\sqrt{3}\cos(x)+2)+\cos(x)(2-\sqrt{2}\sqrt{3}+\sqrt{3}\cos(x))-2\sqrt{2}=0$$

$$\sin(x)(\sqrt{3}\cos(x)+2)+\cos(x)(2-\sqrt{2}\sqrt{3}+\sqrt{3}\cos(x))-2\sqrt{2}=0$$

$$\sin(x)(\sqrt{3}\cos(x)+2)+\cos(x)(\sqrt{3}\cos(x)+2)-\sqrt{2}\sqrt{3}\cos(x)-2\sqrt{2}=0$$

$$(\sqrt{3}\cos(x)+2)(\sin(x)+\cos(x))-\sqrt{2}(\sqrt{3}\cos(x)+2)=0$$

$$(\sqrt{3}\cos(x)+2)(\sin(x)+\cos(x)-\sqrt{2})=0$$

At this point, I think we can just refer to your post on how to solve for the values for $$x$$.

topsquark said:
I'm beginning to think that you are a sadist...

-Dan

Well, I'm usually pretty hard on myself...:o(Tongueout)
 
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