Final answer:
The expression 3y² -5y³ -7y² +7y³ simplifies to -4y² + 2y³ after combining like terms.
Step-by-step explanation:
To simplify the expression and combine like terms, we need to group together terms that have the same variables raised to the same power. Looking at the given expression, 3y² -5y³ -7y² +7y³, we identify that 3y² and -7y² are like terms, as well as -5y³ and 7y³. Simplifying these we get:
- 3y² - 7y² = -4y²
- -5y³ + 7y³ = 2y³
Combining these results yields the simplified expression:
-4y² + 2y³
We can check if this answer is reasonable by ensuring that no like terms have been left uncombined, and the terms we've combined actually contain the same variables raised to the same powers.