Thread: Proving |a+b| = |a|+|b|

Hi guys, I'm doing a case by case proof of



from Spivak, and he says:

When and , we must prove that:



I'm a bit stuck on his line of reasoning, could someone explain why we have to prove the above?

Originally Posted by rowe

I'm doing a case by case proof of
from Spivak, and he says

You cannot prove because it is not true.
So exactly what is the correct statement of this problem?

Typo, sorry. Fixed original post

Originally Posted by rowe

Hi guys, I'm doing a case by case proof of



from Spivak, and he says:

When and , we must prove that:



I'm a bit stuck on his line of reasoning, could someone explain why we have to prove the above?

Hi

If then
and if then

Therefore when and ,