Thread: Is this a valid proof?

Let x be a real number and show that -[-x] is the least integer greater than or equal to x.

Proof:
By definition, [x] is the least integer less than or equal to x and [-x] is the least integer less than or equal to -x.
So we have -x >= [-x]
divide both sides by -1
result => x <= -[-x]

is this sufficient?pr

Originally Posted by evthim

By definition, [x] is the least integer less than or equal to x

Greatest.

Originally Posted by evthim

and [-x] is the least integer less than or equal to -x.
So we have -x >= [-x]
divide both sides by -1
result => x <= -[-x]

You have not shown that -[-x] is the least integer >= x.