find the values of a,b and c of the quadratic equation y=ax^2+bx+c if it passes through the points (1,15), (-1,7), and (0,10).

y=ax^2+bx+c 
(0,10) => c=10 
(1,15) => a+b+10=15 or a+b=5 
(-1,7) => a-b+10=7 or a-b=-3 


adding the two last equations yields 2a=2 so that a=1 
and from the second equation a+b=5 we conclude b=4 


 

:)