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?

What is value of cot² 15° + tan² 15° ?

In a triangle ABC, sin A - cos B - cos C = 0. What is angle B equal to?