Identify the expression under the square root: \( \sqrt{63x^2} \).
Break down the expression under the square root into its prime factors: \( 63x^2 = 9 \times 7 \times x^2 \).
Recognize that \( 9 \) is a perfect square and \( x^2 \) is also a perfect square. Therefore, \( \sqrt{9} = 3 \) and \( \sqrt{x^2} = x \).
Simplify the square root by taking the square root of the perfect squares: \( \sqrt{63x^2} = \sqrt{9} \times \sqrt{7} \times \sqrt{x^2} = 3x\sqrt{7} \).
The simplified form of the radical expression is \( 3x\sqrt{7} \).