What is the value of 2(2 × 1) + 3(3 × 2 × 1) + 4(4 × 3 × 2 × 1) + 5(5 × 4 × 3 × 2 × 1) + .................. + 9(9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1) + 2 ?

If A = {{1, 2, 3}}, then how many elements are there in the power set of A?

If a, b, c are in GP where a > 0, b > 0, c > 0, then which of the following are correct?

1. a², b², c² are in GP

2. $\frac{1}{a}, \frac{1}{b}, \frac{1}{c}$ are in GP

3. $\sqrt {a}, \sqrt{b}, \sqrt{c} $ are in GP

Select the correct answer using the code given below :

If $\frac{a+b}{2}, b, \frac{b+c}{2}$ are in HP, then which one of the following is correct?