1. **State the problem:** Calculate the value of $9^{900}$. 2. **Recall the formula:** For any number $a$ and exponent $n$, $a^n$ means multiplying $a$ by itself $n$ times. 3. **Simplify the base if possible:** Note that $9 = 3^2$, so we can rewrite $9^{900}$ as $(3^2)^{900}$. 4. **Use the power of a power rule:** $(a^m)^n = a^{m \times n}$, so $(3^2)^{900} = 3^{2 \times 900} = 3^{1800}$. 5. **Final expression:** $9^{900} = 3^{1800}$. Since $3^{1800}$ is an extremely large number, it is usually left in this exponential form for simplicity.