Solve the system
{x₁ + 5x₃ + 2x₄ = 7
{x₁ + 5x₃ + 2x₄ = 7
{4x₁ + 20x₃ + 8x₄ = 28
{ + x₂ + 6x₃ + 8x₄ = -5
For this problem, let s be the variable with the smaller index and t be the variable with the larger index.
[x₁] [__] [__] [__]
[x₂] = [__] + s [__] + t [__]
[x₃] [__] [__] [__]
[x₄] [__] [__] [__]
