Is twice a number plus 4 equal 8

If the ratio of sum of the first m and n terms of an ap is m2 : n2 , show that the ratio of its mth and nth terms is (2m − 1) : (2n − 1).

For the inequality |c| < |d| to be true, which of the following must be true?

Find cot x if sin x cot x csc x = √2