The 9th term of an Arithmetic Progression is 8 and the 4th term is 20. Find the first term and the common difference.

Answer 1

There are 5 terms, with a total difference of -12, so d = -12/5

a + 3(-12/5) = 20
a - 36/5 = 20
a = 136/5

So, the sequence is

136/5, 124/5, 112/5, 100/5=20, 88/5, 76/5, 64/5, 52/5, 40/5=8, ...

Answer 2

The sum of the 6 and 8 term of an ap is 142,if the 4 term is 49 calculate the first term