Question 8.18: Prove that for closed polygons, the sum of the exponents (a1...
Prove that for closed polygons, the sum of the exponents \left(\alpha_{1} / \pi\right)-1,\left(\alpha_{2} / \pi\right)-1, \ldots,\left(\alpha_{n} / \pi\right)-1 in the Schwarz-Christoffel transformation (8.9) or (8.10), page 247 , is equal to -2 .
{\frac{d w}{d z}}=A(z-x_{1})^{\alpha_{1}/\pi-1}(z-x_{2})^{\alpha_{2}/\pi-1}\cdot\cdot\cdot(z-x_{n})^{\alpha_{n}/\pi-1} (8.9)
w=A\int(z-x_{1})^{\alpha_{1}/\pi-1}(z-x_{2})^{\alpha_{2}/\pi-1}\cdot\cdot\cdot(z-x_{n})^{\alpha_{n}/\pi-1}d z+B (8.10)
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The sum of the exterior angles of any closed polygon is 2 \pi. Then
\left(\pi-\alpha_{1}\right)+\left(\pi-\alpha_{2}\right)+\cdots+\left(\pi-\alpha_{n}\right)=2 \pi
and dividing by -\pi, we obtain as required,
\left(\frac{\alpha_{1}}{\pi}-1\right)+\left(\frac{\alpha_{2}}{\pi}-1\right)+\cdots+\left(\frac{\alpha_{n}}{\pi}-1\right)=-2