Thank you for your response!
But i did try that way before i posted this topic, and eventually, it can not be solved. I don't know why? Can you figure out where my mistake is, please ! Thanks.
I substituted 2 points (4.8 , 0) and (0 , -5.76) into the equation : " ax^2 + bx = 5.76 ", and i had the system : a(4.8)^2 + 4.8b = 5.76 and a(0) + b(0) = 5.76
And my result is "Math Error" ^^!