Find the general value of `theta` from the equation `sinalpha+sin(alpha+theta)+sin(alpha+2theta)=0`.

Explanation

To solve the equation \( \sin \alpha + \sin(\alpha + \theta) + \sin(\alpha + 2\theta) = 0 \), we can follow these steps:

### Step 1: Rearrange the Equation
We start with the equation:
\[ \sin \alpha + \sin(\alpha + \theta) + \sin(\alpha + 2\theta) = 0 \]
We can rearrange this as:
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