Get a common denominator for the second expression, so the addition can be done above a single denominator.
( 2x2 + 3 )( 2x + 1) = 4x3 + 2x2 + 6x + 3
so the second expression can be rewritten as 4x3 + 2x2 + 6x + 3 4
———————— + ———
2x + 1 2x + 1
when you add those together, it is 4x3 + 2x2 + 6x + 3 + 4 4x3 + 2x2 + 6x + 7
—————————— and adding the 3 + 4 we obtain ————————
2x + 1 2x + 1
This is the same as the first expression, so the two are equivalent for every
value (not just 10) except x = –1/2 because when x = –1/2 the denominator
becomes zero and Rule No. 1 is "Thou shall not divide by zero."
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