by simplifying the expression 5 radical ab * 3 radical a^B^ what is the answer in radical notation?

Did you mean 5*sqrt(ab) * 3*sqrt(ab)?

If so, the answer is 15ab. Sqrt means
square root.

5*(ab)^(1/2) * 3*(ab)^(1/2) = 15(ab)^1 =
15ab.