How to bring bracket number format for negative value in mac excel 2011 ? getting trouble..

Have you tried the Format ➙ Cell option:

Only parentheses can be used and not brackets, [ ] or { }.

If you mean parentheses it is gone with Yosemite. See this link:

Parentheses for negative numbers in Excel 2011

With Yosemite that feature is gone

Not true. As you can see from my screenshot using ( ) for negative numbers with Excel 2011 is well and working with Yosemite. These screenshot confirm it.

It might have been the last updater that brought it back:

The OP should use the Help ➙ Check for updates and run any and all available that he hasn't done so previously.

That's v2008, in v2011 (as the OP uses) it is gone.

Outlook 2011 version 14.5.1

You're right. Tunnel vision gave me 2008. 😟

🙂 I know the feeling.