[tex]\frac{a+2}{2} = \frac{1}{2} a t^2 \\\\\frac{a}{2} + 1 = \frac{1}{2} a t^2 / -\frac{a}{2} \\\\\frac{1}{2} a t^2 -\frac{a}{2} = 1 \\\\\frac{1}{2}a(t^2 -1) = 1 / \cdot 2 \\a(t^2 -1) = 2 / :(t^2-1)\\a = \frac{2}{t^2-1}[/tex]
