If the x-intercepts are x=-2 and x=1 we have that the factorized form of the function is
[tex]f(x)=k(x+2)(x-1)[/tex]
if we want that the point (2,8) belongs to the graph we have that
[tex]\begin{gathered} 8=k(4)\cdot(1)=4k \\ k=2 \end{gathered}[/tex]
therefore the function is
[tex]f(x)=2(x+2)(x-1)=2\cdot\lbrack x^2+x-2\rbrack=2x^2+2x-4[/tex][tex]f(x)=2x^2+2x-4[/tex]
