diff --git a/rtchallenge/src/matrices.rs b/rtchallenge/src/matrices.rs
index 3d3c35f..2d6d96e 100644
--- a/rtchallenge/src/matrices.rs
+++ b/rtchallenge/src/matrices.rs
@@ -8,6 +8,38 @@ pub struct Matrix4x4 {
     m: [[f32; 4]; 4],
 }
 
+pub struct Matrix2x2 {
+    m: [[f32; 2]; 2],
+}
+impl Matrix2x2 {
+    /// Create a `Matrix2x2` with each of the given rows.
+    pub fn new(r0: [f32; 2], r1: [f32; 2]) -> Matrix2x2 {
+        Matrix2x2 { m: [r0, r1] }
+    }
+}
+impl Index<(usize, usize)> for Matrix2x2 {
+    type Output = f32;
+    fn index(&self, (row, col): (usize, usize)) -> &Self::Output {
+        &self.m[row][col]
+    }
+}
+
+pub struct Matrix3x3 {
+    m: [[f32; 3]; 3],
+}
+impl Matrix3x3 {
+    /// Create a `Matrix3x2` with each of the given rows.
+    pub fn new(r0: [f32; 3], r1: [f32; 3], r2: [f32; 3]) -> Matrix3x3 {
+        Matrix3x3 { m: [r0, r1, r2] }
+    }
+}
+impl Index<(usize, usize)> for Matrix3x3 {
+    type Output = f32;
+    fn index(&self, (row, col): (usize, usize)) -> &Self::Output {
+        &self.m[row][col]
+    }
+}
+
 impl From<[f32; 16]> for Matrix4x4 {
     fn from(t: [f32; 16]) -> Self {
         Matrix4x4 {
@@ -241,6 +273,23 @@ impl Index<(usize, usize)> for Matrix4x4 {
 mod tests {
     use super::*;
 
+    #[test]
+    fn construct2x2() {
+        let m = Matrix2x2::new([-3., 5.], [1., -2.]);
+
+        assert_eq!(m[(0, 0)], -3.);
+        assert_eq!(m[(0, 1)], 5.);
+        assert_eq!(m[(1, 0)], 1.);
+        assert_eq!(m[(1, 1)], -2.);
+    }
+    #[test]
+    fn construct3x3() {
+        let m = Matrix3x3::new([-3., 5., 0.], [1., -2., -7.], [0., 1., 1.]);
+
+        assert_eq!(m[(0, 0)], -3.);
+        assert_eq!(m[(1, 1)], -2.);
+        assert_eq!(m[(2, 2)], 1.);
+    }
     #[test]
     fn construct4x4() {
         let m = Matrix4x4::new(