Question

The ninth term of an ap is 7-4n find the common difference

Answer 1

Let the first term be a.

The ninth term is a+8d

As per the question a+8d = 7-4n.

8d = 7-4n-a

d = 7-4n-a/8 .

Hope helped! ^^

Answer 2

The ninth term of an AP is 7 - 4n.
$a_{9} = 7 - 4n$
a + 8d = 7 - 4n
8d = 7 - 4n - a
d = (7-4n-a)/8

If your question is as follows,
If nth term of an AP is 7 - 4n,find the common difference. (I guessed as I have this problem in my book)

This is the solution.

$a_{n} = 7 - 4n$

$a_{1} = 7 - 4(1) = 7 - 4 = 3$
$a_{2} = 7 - 4(2} = 7 - 8 = -1$
$a_{3} = 7 - 4(3) = 7 - 12 = -5$

$d = a_{2} - a_{1} = -1 - 3 = -4$

Common difference,d = -4