## Calculus (3rd Edition)

| x | - | y | $\leq$ | x - y |
| x - y | + | y | $\geq$ | x - y + y | = |x| by triangle inequality; So, | x - y | + | y | $\geq$ | x | ; subtracting both sides by | y |, we get: | x - y | $\geq$ | x | - | y |