For this problem we can represent the situation as a rectangle triangle.
x: depth of water.
40: Base. "Antonio pulls the lily to one side, keeping the stem straight, until the blossom touches the water at a spot"
x + 8: Hypotenuse. "He notices water lily sticking straight up from the water, whose blossom is 8 cm above the water's surface." Antonio pulls the lily to one side, keeping the stem straight, until the blossom touches the water at a spot".
By the Pythagorean theorem we have:
x ^ 2 + 40 ^ 2 = (x + 8) ^ 2
Clearing x:
x ^ 2 + 1600 = x ^ 2 + 16x + 64
x ^ 2 - x ^ 2 = 16x + 64 - 1600
0 = 16x -1536
1536 = 16x
1536/16 = x
x = 96
answer:
1) x ^ 2 + 40 ^ 2 = (x + 8) ^ 2
2) the depth of the water is
x = 96
