Why don't you try a little harder?

Question

Why not try a little harder?

Why don't we try a little harder?

Let's try a little harder.

Let's try a little harder, shall we?

Shall we try a little harder?

How about trying a little harder?

What about trying a little harder?

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Do the sentences above have the same meaning?

1. Why not try a little harder?
2. Why don't you try a little harder?
3. Why don't we try a little harder?

Does #1 mean #2 or #3?