Answer:
•3✓7
✓3.✓21
=✓3×✓3✓7
=3✓7
3rd answer is correct
Step-by-step explanation:
√3 × √21
√3 × √(7 × 3)
√( 3 × 3 × 7 )
√ ( 3 × 3 ) × √7
3√7
