Question

Jeongin kicks a stone off the edge of a tall cliff. The distance, d, between the rock and the ground t seconds after being kicked is d = -16t² -6t +480. How many seconds go by before the rock is at height of 424 feet above the ground?

mkay so I tried to solve it, but the factoring seems really off when I tried to find t. Is it really solvable or am I missing something? help would be appreciated thank youu :)​

Answer 1

• 1.693 seconds

Explanation:

Given function

• d(t) = -16t² -6t +480
• Find t, when d = 424

Solution

• -16t² -6t +480 = 424
• -16t² -6t +480 - 424 = 0
• -16t² -6t + 56 = 0
• 8t² +3 t - 28= 0
• t = (- 3± √3² -4*8*(-28))/16
• t = (-3±√905)/16
• t = 1.693 seconds (positive solution)