Final answer:
The given polynomial expression (5r+9r³)-(4r³+7r) simplifies to 5r³ - 2r by combining like terms.
Step-by-step explanation:
We need to solve the following expression by combining like terms: (5r+9r³)-(4r³+7r). To do this, we first recognize that 5r and 7r are like terms, as are 9r³ and 4r³. We combine these like terms by adding or subtracting coefficients.
The expression simplifies to 5r - 7r for the r terms, which equals -2r. For the r³ terms, it simplifies to 9r³ - 4r³, resulting in 5r³.
The final simplified expression is 5r³ - 2r.