You can put this solution on YOUR website! .
Find the first term of an Arithmetic sequence , whose 3rd term is 20 and its 6th term is - 4.
~~~~~~~~~~~~~~
Between the 3rd term and 6th term, there are 3 gaps of equal size on the number line.
The size of each gap is = = 8 units.
Hence, the common difference of this arithmetic sequence is d = -8
(it is exactly the gap size, but the sequence is decreasing, so the common difference is negative).
Next, the 1st term is 2 gaps backward from the 3rd term,
so, the 1st term is = 20 - 2*(-8) = 20 + 16 = 36.
ANSWER. First term of this arithmetic progression is 36.
CHECK. = = 36 + 5*(-8) = 36 - 40 = -4. ! correct !
