The mid-point of the line segment joining the points (1, -6), (3, x) is (2, 6). The value of x is :

1. 1

2. 2

3. 18

4. -18

If sin² A + cos² A + 4x sin² A cos² A = 8 sin² A cos² A + 1; the value of x is :

1. 2

2. 1

3. $\dfrac{1}{2}$

4. -2

If the discriminant of quadratic equation ax² + bx + c = 0 is equal to zero, then the two equal roots are :

1. $\dfrac{b}{2a} \text{ and } \dfrac{b}{2a}$

2. $-\dfrac{b}{2a} \text{ and } -\dfrac{b}{2a}$

3. $\dfrac{a}{2b} \text{ and } \dfrac{a}{2b}$

4. $-\dfrac{a}{2b} \text{ and } -\dfrac{a}{2b}$

If n^th term of an A.P. is 6n - 15, then its common difference is :

1. 6

2. -6

3. 12

4. -12