Numbers help school

[real scaffold]

Hello, I can help you perfecly.

[real scaffold]

you can solve this problem as following step.
first there are any number {d}: |a-d|<2/&,
we can express this |a-b| with below expression.
|a-b| = |(a-d)+(d-b)| <= | a-d | + |b-d| < &/2 + &/2 = &

As a result this problem is proved .
Okay

[formal delta]

.close