21-28 Simplify: 21) \( 2 \sqrt{125 v} \)

Step 1 ：\( 2\sqrt{125v} = 2\sqrt{5^3v} \)

Step 2 ：\( 2\sqrt{5^3v} = 2\cdot5\sqrt{5v} \)

Step 3 ：\( 2\cdot5\sqrt{5v} = 10\sqrt{5v} \)