Final answer:
To rewrite the expression -8x^2 + 3xy - 9x - 3 as a sum, group the like terms together.
Step-by-step explanation:
To rewrite the expression -8x^2 + 3xy - 9x - 3 as a sum, we group like terms together. The expression can be rewritten as (-8x^2) + (3xy) + (-9x) + (-3).
When we group the terms with the same variable and exponent, we get the sum -8x^2 + 3xy - 9x - 3.