Answer:
2√21
Step-by-step explanation:
√81 is √4 times √21
Since √4 is a perfect square, √4 = 2
We are left with 2 times √21
√84
84 can be written as 4 × 21.
√(4 × 21)
Distribute the square root to both terms.
√4 × √21
4 is a perfect square.
2 × √21
