`The upper triangular system
`

`The upper triangular system is
`

`From the last equation . We substitute this value in equation 2
`

`Finally, we substitute the known values of , in equation 1
`

`In short, we start with the last equation and find . Then,
we move backwards through the equations; at each step we
substitute the known values
in the current
equation , and compute the value of . This process is called
backward substitution.
`