1. Solution sets
   1. Unique solution
      1. For every x is one solution, and for every solution is one x
   2. Infinite solutions
      1. xn=a, where xn=0 and a=0
      2. x1+x2=a where x1, x2 and a are an element of R
   3. No solution
      1. xn=a, where xn=0 and a is not 0
2. Description of R^n
   1. n, is the number of rows
   2. Always with 1 column
3. Forms
   1. Echelon form
      1. All nonzero rows are above any rows of all zeros
      2. Each leading entry of a row is in a column to the right of the leading entry of the row above
      3. All entries in a column below a leading entry are zeros
   2. Reduced echelon form
      1. All nonzero rows are above any rows of all zeros
      2. Each leading entry of a row is in a column to the right of the leading entry of the row above
      3. All entries in a column below a leading entry are zeros
      4. The leading entry in each non zero row is 1
      5. Each leading 1 is the only non zero entry in its column
4. Notations
   1. Rules
      1. Topic
      2. Topic
      3. Topic
      4. Topic
   2. If A is an m*n matrix
      1. m is the number of rows
      2. n is the number of columns