prove that `a^2sin2B+b^2sin2A=4Delta`

Explanation

To prove that \( a^2 \sin 2B + b^2 \sin 2A = 4\Delta \), we will follow these steps:

### Step 1: Express \( a \) and \( b \) in terms of \( r \) and angles
We know that in a triangle, the sides \( a \) and \( b \) can be expressed as:
\[ a = 2r \sin A \quad \text{and} \quad b = 2r \sin B \]

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