$\displaystyle f(x)= \frac{1}{2}(x+3)(x-1)$\displaystyle f(x)= \frac{1}{2}(x+3)(x-1)

$\displaystyle f(x)= \frac{1}{2}(x-3)(x+1)$\displaystyle f(x)= \frac{1}{2}(x-3)(x+1)

$\displaystyle f(x)= \frac{1}{2}(x+3)(x-1)$\displaystyle f(x)= \frac{1}{2}(x+3)(x-1)

$\displaystyle f(x)= -\frac{1}{2}(x-3)(x+1)$\displaystyle f(x)= -\frac{1}{2}(x-3)(x+1)