To get ² hold down "alt" while typing 253 on the key pad ar the far right of
your keyboard, (not the numbers above the letter keys).  The get ³ use 0179.

The opposite of

-x²+27x-6

is either

-(x²+27x-6) <-- putting it in parentheses with a - before it.

0r

x²-27x+6    <-- changing all the signs.

or you can rearrange the terms:

6-27x+x²

or you can factor x out of the first two terms of x²-27x+6: 

x(x+27)+6

There are many ways to get an equivalent expression for the
opposite of -x²+27x-6

Edwin