Simplify the exponential expression. \[ \left(3 x^{8}\right)\left(3 x^{9}\right) \]

To simplify the exponential expression \((3 x^{8})(3 x^{9})\), start by multiplying the coefficients and then add the exponents of the like bases. First, multiply the coefficients: \(3 \times 3 = 9\). Next, for the \(x\) terms, add the exponents: \(8 + 9 = 17\). Putting it all together, you get: \[ 9 x^{17} \] So, the simplified expression is \(9 x^{17}\).