Given : r(x)=3x3+4x2+5x−7
In the given polynomial r(x)=3x3+4x2+5x−7, highest power of the variable x is 3 so the degree of the polynomial is 3.
We know that a polynomial of degree 3 is konwn as cubic polynomial.
Hence, polynomial r(x)=3x3+4x2+5x−7 is a cubic.