To simplify the given expression:

$(2x^2 - 7x + 5) + (6x^2 + 9x - 10),$

we combine like terms step by step:

1. Combine the $x^2$ terms:
   $2x^2 + 6x^2 = 8x^2$.

2. Combine the $x$ terms:
   $-7x + 9x = 2x$.

3. Combine the constant terms:
   $5 - 10 = -5$.

Final Simplified Expression:

$8x^2 + 2x - 5.$

Let me know if you'd like a breakdown of the steps!

Related Questions:

1. How do you simplify an expression with multiple variables?
2. What are like terms, and why are they important in simplifying expressions?
3. How do you add or subtract polynomials?
4. What happens when you combine terms with different powers of $x$?
5. Can you factorize $8x^2 + 2x - 5$?

Tip:

Always group like terms (same variable and same exponent) to simplify polynomials efficiently.