simplify the radical expression by rationalizing the denominator.

4/*21

* means square root

multiply top and bottom by sqrt(21)

To simplify the radical expression 4/√21 by rationalizing the denominator, we can multiply the numerator and denominator by √21. This is done to eliminate the radical in the denominator.

(4/√21) * (√21/√21)

Multiplying the numerators and denominators together gives us:

(4 * √21) / (√21 * √21)

Simplifying further:

(4√21) / (√(21*21))

The square root of (21*21) is equal to 21:

(4√21) / 21

Therefore, the simplified expression is 4√21/21.

To simplify the radical expression 4/√21 by rationalizing the denominator, follow these steps:

Step 1: Write the expression as a fraction: 4/√21.

Step 2: To rationalize the denominator, we need to eliminate the radical (√) in the denominator.

Step 3: Multiply the numerator and denominator by the conjugate of the denominator. The conjugate of √21 is (-√21). Multiply both the numerator and denominator by (-√21):

(4/√21) * (-√21) / (-√21)

Step 4: Simplify the expression:

(-4√21) / (-1 * √21)
= (-4√21) / (-√21)
= 4

Therefore, the simplified radical expression after rationalizing the denominator is 4.