the first four terms of an arithmetic progression whose first term is -2 and the common diff. is -2 is

-20

Step-by-step explanation:where first term =a and common difference=d

     =

     =

     =

18

step-by-step explanation:

draw the shape and you will see that f and k are actually at adjacent vertices (points of the hexagon that are neighboring).   so find the distance between (1,2) and (4,2).   that is easy since (1,2) and (4,2) is just a vertical distance to count, which is 3.   it is a regular polygon which means all sides are congruent.   you have 6 sides (hexa) so multiply 6 by 3 to receive 18.