Write the first four terms of a decreasing Arithmetic Sequence. Use this to describe, in your own words, how to write the formula for the sequence. Then use the formula to calculate the 20th term. Show all work.

16.80 times .20= 3.36

step-by-step explanation:

the diagram shows you   triangle def with de=4, df=9 and de≠df≠ef.

the sum of the lengths of two triangles' sides are always greater than the length of the third side:

substitute sides lengths:

then 5< ef< 13 (option 3 is true).

def is a scalene triangle with all sides of different lengths (option 5 is true, option 2 is false).

answer: correct choices are 1, 3 and 5