To solve the inequality \(8^{\frac{x}{3}} < 64^{\frac{x+7}{2}}\), we can start by expressing both sides with the same base. Notice that \(8 = 2^3\) and \(64 = 2^6\). This allows us to rewrite the inequality in terms of base 2. Then, we can simplify the exponents and solve for \(x\).
Step 1: Rewrite the inequality with the same base
Given the inequality \(8^{\frac{x}{3}} < 64^{\frac{x+7}{2}}\), we start by expressing both sides with the same base. Notice that \(8 = 2^3\) and \(64 = 2^6\). Thus, we can rewrite the inequality as:
\[
(2^3)^{\frac{x}{3}} < (2^6)^{\frac{x+7}{2}}
\]
Step 2: Simplify the exponents
Next, we simplify the exponents:
\[
2^x < 2^{3(x+7)}
\]
This simplifies to:
\[
2^x < 2^{3x + 21}
\]
Step 3: Solve the inequality
Since the bases are the same, we can compare the exponents:
\[
x < 3x + 21
\]
Subtract \(x\) from both sides:
\[
0 < 2x + 21
\]
Subtract 21 from both sides:
\[
-21 < 2x
\]
Divide by 2:
\[
-\frac{21}{2} < x
\]
Final Answer
Thus, the solution to the inequality is:
\[
x \in \left( -\frac{21}{2}, \infty \right)
\]
\[
\boxed{x \in \left( -\frac{21}{2}, \infty \right)}
\]