Answer:
1 seconds after being thrown, the stone reaches its max height
Step-by-step explanation:
The parabolic (quadratic) equation is:

Lets expand this in the form
, so we have:

We can say the values of a,b, and c, now to be:
a = -5
b = 10
c = 40
The number of seconds at which the max would occur is given by the point, x, at:

We know a and b, let's find the seconds, x,

Hence,
1 seconds after being thrown, the stone reach its max height
Answer:
y = 3x - 10
Step-by-step explanation:
Starting with 3x - y = 10, add y to both sides:
3x = 10 + y
Then subtract 10 from both sides:
3x - 10 = y
If you switch the sides of the equation, it can also be written as:
y = 3x - 10
4y = -23 + 39
4y = 16
y = 4
Sub y = 4 into equation 2
7x + 6(4) = -39
7x + 24 = -39
7x = -39-24
7x = -63
x = -9
x = -9
y = 4
If that’s meant to be x^2 - 6x - 16
Then factorise to (x+2)(x-8)
So x intercepts are -2 and 8