# Find the area!

**Geometry**Level 5

\[S=\{(x,y,z) \in \mathbb{R}^3: x^2+y^2+z^2=1\}\]

Let \(S\) be the surface of a unit sphere centered at the origin.

Let \(F\) be a subset of \(S\). Suppose that there exist three subsets \(F_1,F_2,F_3 \) of \(S\), each of which is obtained by rigidly rotating the set \(F\) around the origin such that:

- These three sets are pairwise disjoint, i.e., \[F_i\cap F_j = \phi, i\neq j\]
- Their union spans the entire surface of the sphere, i.e.,

\[F_1\cup F_2 \cup F_3=S\]

Find the area of any such set \(F\) satisfying the above conditions.

**P.S.**
Rotation is defined in the usual way:
\[F_i=\{(x,y,z): \exists (a,b,c) \in F \text{ s.t. } (x,y,z)'=Q_i (a,b,c)'\} \]
for some orthonormal matrix \(Q_i,i=1,2,3\).

**Your answer seems reasonable.**Find out if you're right!

**That seems reasonable.**Find out if you're right!

Already have an account? Log in here.