(a)
Since, $y = x^{2} - 5x + 6$
$\therefore\ \ \ \ \ \ \frac{dy}{dx} = 2x - 5$
Now, $m_{1} = \left( \frac{dy}{dx} \right)_{(2,\ 0)} = 4 - 5 = - 1$
And $m_{2} = \left( \frac{dy}{dx} \right)_{(3,\ 0)} = 6 - 5 = 1$
Now, $m_{1}m_{2} = - 1 \times 1 = - 1$
Hence, angle between the tangents is $\frac{\pi}{2}$