9)
Let n be a positive integer.
From there, work out the long division, and you get a result with no remainder, hence 12 is a factor of the given expression.
[ (3n^2 + 6n) / 12 ] = { [(n^2) / 4] + (n/2) } .
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11.
( x^2 - 5x + 8 ) = [ (x - 2.5)^2 + 1.75 ]
and the right-hand side is...