Which of the following is(are) NOT the square of a 3 $$ \times $$ 3 matrix with real entries?

If a chord, which is not a tangent, of the parabola y² = 16x has the equation 2x + y = p, and mid-point (h, k), then which of the following is(are) possible value(s) of p, h and k?

For a real number $$\alpha $$, if the system

$$\left[ {\matrix{ 1 & \alpha & {{\alpha ^2}} \cr \alpha & 1 & \alpha \cr {{\alpha ^2}} & \alpha & 1 \cr } } \right]\left[ {\matrix{ x \cr y \cr z \cr } } \right] = \left[ {\matrix{ 1 \cr { - 1} \cr 1 \cr } } \right]$$

of linear equations, has infinitely many solutions, then 1 + $$\alpha $$ + $$\alpha $$² =

The sides of a right angled triangle are in arithmetic progression. If the triangle has area 24, then what is the length of its smallest side?