Question

Khan-academy help please

Answer 1

Hello,

x = 10

Explanation:

`-(-10)/(2(1)/(2) ) = (10)/(1) = 10`

or :

d(0) = 0

and

d(20) = 0

`(0 + 20)/(2) = 10`

Answer 2

Solve for x^2/2 - 10x = 0

<=> x^2 - 20x = 0

<=> x(x - 20) =0

<=> x = 0(invalid), x = 20

=> After 20s, Rui reaches his lowest altitude