The lines are parallel, because they have the same gradient but are just in different positions ie. y = x-9.
A6 = -8
a15= -62
There are (15 - 6) terms in between, therefore 9 terms in between.
-8 to -62 ... there is a difference of 54
54 ÷ 9 = 6
Therefore it gets -6 each term.
a6 = -8, a7= -14, a8 = -20 ......
Sequence will look like this:
Term 1: 20 --------- 20 + 5(0)
Term 2: 25 --------- 20 + 5(1)
Term 3: 30 --------- 20 + 5(2)
Term 4: 35 --------- 25 + 5(3)
ETC.
It cab noted that the numbers in the bracket (that is, 0, 1, 2, 3, 3, etc) = n-1
Then, the explicit formula will be;
an = 20 + 5(n-1).
The correct answer is D.
