# Substitute ME!

**Geometry**Level pending

The two sides of a triangle measures 18 and 14 units with an angle of \(10.84^0\). Evaluate sin \(\frac{π}{a}\) - sin \(\frac{2π}{a}\) - sin \(\frac{3π}{a}\) - . . . - sin \(\frac{8π}{a}\) + sin \(\frac{9π}{a}\), if *a* is equal to the third side of the triangle.