f(x) = 2 cosx + 1 is concave down on [0, 1]. What is the estimate for f(3) using the local linear approximation for f at x = π/2? Give an exact answer (no rounding). (I need the steps)

Suppose you are analyzing the relationship between time and distance given in a table,and there are 4 values for each quantity.you divide distance 2 minus distance 1 by time 2 minus time 1.you then divide distance 4 minus distance 3 by time 4 minus time 3 and get a different answer.what can you say about the relationship?