Answer:
Before coming back up to the surface the maximum depth, Cassidy went was 6.25 ft. below the water surface
Step-by-step explanation:
The height of Cassidy's diving platform above the water = 6 ft.
The equation that models her dive is d = x² - 7·x + 6
Where;
d = Her vertical position or distance from the water surface
x = Here horizontal distance from the platform
At Cassidy's maximum depth, we have;
dd/dx = d(x² - 7·x + 6)/dx = 2·x - 7 = 0
x = 7/2 = 3.5
∴ At Cassidy's maximum depth, x = 3.5 ft.
The maximum depth, = d(3.5) = 3.5² - 7 × 3.5 + 6 = -6.25
The maximum depth, Cassidy went before coming back up to the surface = = -6.25 ft = 6.25 ft. below the surface of the water.