√16< √21 <√25
4< √21 <5 | * (-1) <0
-4> - √21 > -5
-5 < -√21 < -4
-5 +1< -√21+1 < -4+1
-4<1 -√21 < -3
√16< √21 <√25
4< √21 <5 | * (-1) <0
-4> - √21 > -5
-5 < -√21 < -4
-5 +1< -√21+1 < -4+1
-4<1 -√21 < -3