2.| Root number 2- Root number 3| =√3-√2

3 (1)√7 is between 2 and 3 on the number axis.

(2)2.645 & lt； √7 & lt； 2.646

4.V = 4\3∏ R 3 times 2 = 18 times 4\3∏.

The bottom area of the circular iron column is equal to 18 times 4 \ 3 \ divided by 5.

The radius of the bottom surface of the circular iron column is equal to 18 times 4 \ 3 \ divided by 5 divided by pai.

The root sign √4.8 is approximately equal to 2. 19.