Once again, the textbook from which this question comes from has no prior example which I could reference to even possibly answer this.
If , show that when .
My Prof. is a true sadist...
Through other online sources, I've come up with this so far. I suspect, however, that it has some pieces missing.
If we square , we get .
This says that lies inside a circle of radius around the origin.
Using the triangle inequality, (which is )
The condition means that separately, , and are all less than .
Therefore, .
If there are any errors in this, I'd appreciate it if they were pointed out.