Hello, r_maths!
I just need to know, how to find equation of a parabola
and put it in the form of ax² + bx + c just from reading the graph.
I can do this for graphs where it cuts the xaxis.
But for graphs were it doesn't cut the xaxis,
how would you find the equation? Code:

* *

A o(0,18) C o(4,18)
 * *
 * B *
 o
 (2,10)


  +           

I assume that point B(2,10) is the vertex of the parabola.
The parabola is symmetric to its axis: x = 2.
. . Hence, there is a point C(4,18) symmetric to A(0,18).
The parabola has the general equation: .y .= .ax² + bx + c
We can evaulate these coefficients, using the three given points.
(0,18): .a·0² + b·0 + c .= .18 . → . c = 18
(2,10): .a·2² + b·2 + 18 .= .10 . → . 4a + 2b .= .8 .[1]
(4,18): .a·4² + b·4 + 18 .= .18 . → . 16a + 4b .= .0 .[2]
Multiply [1] by 2: . 8a  4b .= .16
. .  . . . .Add [2]: .16a + 4b .= .0
And we get: .8a = 16 . → . a = 2
Substitute into [1]: .8 + 2b .= 8 . → .b = 8
Therefore: .y .= .2x²  8x + 18