Given the image over total a (- 1,0), B (3,0), C (1,8) of quadratic function f (x)
Let f (x) = ax ^ 2 + BX + C
Because the quadratic function passes a (- 1,0), B (3,0), C (1,8), so
f(-1)=a(-1)^2+b*(-1)+c=0
f(3)=a*3^2+b*3+c=0
f(3)=a*1^2+b*1+c=8
The equations are composed of the above three equations
a=-2,b=4,c=6
So the expression of quadratic function is changed to
f(x)=-2x^2+4x+6
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