4a+2b+c=0 (1)
16a-4b+c=0(2)
a+b+c=15(3)
(2)-(1)
12a-6b=0
2a-b=0 (4)
(1)-(3)
3a+b=-15 (5)
(4)+(5)
5a=-15
所以a=-3
b=2a=-6
c=15-a-b=24
4a+2b+c=0 (1)
16a-4b+c=0(2)
a+b+c=15(3)
(2)-(1)
12a-6b=0
2a-b=0 (4)
(1)-(3)
3a+b=-15 (5)
(4)+(5)
5a=-15
所以a=-3
b=2a=-6
c=15-a-b=24