How to prove triangle inequality?

50 Views Asked by At

How would I prove the triangle inequality for any three points a,b,c in the plane? The inequality needed to prove is $||a-b|| ≤ ||a-c|| + ||c-b||$

It throws me off when the subtractions are included. Please help.

1

There are 1 best solutions below

0
On

In the Euclidean norm, we have $\|a+b\|\leq \|a\| +\|b\|$.

Then $\|a-b\| = \| (a-c) + (c-b)\|$ and so by the above inequality, $\|a-b\| \leq \| a-c |+ \|c-b\|$.