已知三点坐标,求抛物线方程,比如(15,20.3) (35,30.7 )( 50,36.6),

y=ax²+bx+c
所以
225a+15b+c=20.3 (1)
1225a+35b+c=30.7 (2)
2500a+50b+c=36.6 (3)
(2)-(1)
1000a+20b=10.4
所以50a+b=0.52 (4)
(3)-(2)
1275a+15b=5.9
所以85a+b=59/150 (5)
(5)-(4)
35a=-19/150
a=-19/5250
b=59/150-85a=368/315
c=20.3-225a-15b=377/105
所以y=-19x²/5250+368x/315+377/105