Question

how to take out the value of root 21

Answer 1

✔Well done for the question:

▶21=3⋅7 has no square factors, so √21 cannot be simplified.

▶√21≈4.58257569495584000658 is an irrational number whose square is 21.

⬛Explanation:

➡√21=√3⋅7 has no square factors that can be 'moved outside the square root sign'.

▶For example √12=√22⋅3=√22√3=2√3

▶So √21 cannot be simplified.

▶It can't be expressed as a rational number (fraction).

➡So the best we can do with normal notation is to either stick with √21 or give an approximation, such as √21=4.58.
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