Matrix A = $\begin{bmatrix$}[r] 6 & 9 \ -4 & k \end{bmatrix} \text{ such that } A^2 = \begin{bmatrix}[r] 0 & 0 \ 0 & 0 \end{bmatrix}. Then k is :

1. 6

2. -6

3. 36

4. ±6

If the sum of n terms of an arithmetic progression S_n = n² - n, then the third term of the series is :

1. 2

2. 4

3. 6

4. 9

In the adjoining diagram, G is the centroid of △ ABC. A(3, -3), B(2, -6), C(x, y) and G(5, -5). The coordinates of point D are :

1. (2, -6)

2. (3, -6)

3. (6, -6)

4. (10, -6)

In the given diagram, O is the origin and P is the mid-point of AB. The equation of OP is :

1. y = x

2. 2y = x

3. y = 2x

4. y = -x