What is cot 2x cot 4x - cot 4x cot 6x - cot 6x cot 2x equal to

If M is the mean of n observations x₁ - k, x₂ - k, x₃ - k, _ _ _, x_n - k, where k is any real number, then what is the mean of x₁, x₂, x₃, _ _ _, x_n?

What is the sum of deviations of the variate values 73, 85, 92, 105, 120 from their mean?

Let x be the HM and y be the GM of two positive numbers m and n. If 5x = 4y, then which one of the following is correct?