# Modern Geometry

1. Dec 14, 2009

### mrs.malfoy

Let $$\theta$$ be the angle between the diagonal of the unit cube in $$R^{n}$$ and one of its axes.

Find

lim $$\theta$$ (n)
$$_{n\rightarrow\infty}$$

2. Dec 14, 2009

### Rasalhague

You can represent an edge as a unit vector along the x-axis, (1,0,0), and the diagonal as the vector (1,1,1). Consider the definition of the dot product

$$\mathbf{a} \cdot \mathbf{b}= a_{1}b_{1}+a_{2}b_{2}+...+a_{n}b_{n} = \left \| a \right \| \left \| b \right \| cos \; \theta$$

Since we know a = (1,0,0,...) and b = (1,1,1,...), we can solve for $\theta$ in terms of n. To find the limit as n approaches infinity, just try it out with very big numbers.