Answer:
–x² + 12x + 5
Explanation:
x² + 3x
–2x² + 9x + 5
The sum of the above expression can be obtained as follow:
.... x² + 3x
+ –2x² + 9x + 5
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
–x² + 12x + 5
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
Thus, the sum of x² + 3x and –2x² + 9x + 5 is –x² + 12x + 5