Answer:
see below
Step-by-step explanation:
1. (x² - 4x - 10) + (x² - 9x + 3)
= x² - 4x - 10 + x² - 9x + 3
= x² + x² - 4x - 9x + 3 - 10
<h3>= 2x² - 13x - 7
</h3>
4. (3x² - x + 1) + (15 - 9x - 2x²)
= 3x² - x + 1 + 15 - 9x - 2x²
= 3x² - 2x² - x - 9x + 1 + 15
<h3>= x² - 10x + 16
</h3>
7. (6 - 2x + 7x²) - (10x - 3 + 3x²)
= 6 - 2x + 7x² - 10x + 3 - 3x²
= 7x² - 3x² - 2x - 10x + 6 + 3
<h3>= 4x² - 12x + 9</h3>