sample testing

$$\sum_{i=0}^n i^2 = \frac{(n^2+n)(2n+1)}{6}$$ $$\cos(θ+φ)=\cos(θ)\cos(φ)−\sin(θ)\sin(φ)$$ $$(\nabla_X Y)^k = X^i (\nabla_i Y)^k = X^i \left( \frac{\partial Y^k}{\partial x^i} + \Gamma_{im}^k Y^m \right)$$