To solve the given problem, we need to multiply and simplify the square roots. We will use the property of square roots that \(\sqrt{a} \cdot \sqrt{b} = \sqrt{a \cdot b}\).
Step 1: Define the Expressions
We start with the given expressions:
\[
\sqrt{7 x^{2}} \quad \text{and} \quad \sqrt{8 x^{7}}
\]
Next, multiply the simplified expressions:
\[
\sqrt{7} \cdot x \cdot 2\sqrt{2} \cdot x^{3} \cdot \sqrt{x} = 2\sqrt{14} \cdot x \cdot x^{3} \cdot \sqrt{x} = 2\sqrt{14} \cdot x^{4} \cdot \sqrt{x}
\]
Step 4: Combine and Simplify
Combine the terms to get the final simplified expression:
\[
2\sqrt{14} \cdot x^{4} \cdot \sqrt{x} = 2\sqrt{14} \cdot x^{4.5} = 2\sqrt{14} \cdot x^{\frac{9}{2}}
\]