(2) According to Pythagorean theorem, AB2=AC2+BC2,∴√ (root number) ac2+bc2 =√ 2.12+2.82 = 3.5 (cm).

(3) Let the intersection point C be CD⊥AB and the vertical foot D, and use AB CD = AC BC, ∴ 3.5xcd = 2. 1x2.8 and CD = 1.68 (cm) with equal areas.

10: Solution: If the depth is x feet, the length of reed is (x+ 1) feet. According to Pythagorean theorem, it is x2+(10/2) 2 = (x+1) 2.

The solution is x= 12. ∴x+ 1= 13 (feet)