Question

If the sum of 8th and 9th terms of an AP is 72 and the 4th term is -6, what is the common difference

Answer 1

let d be common differences.

8th term of a ap is a given by
a+7d
9th term of a ap is a given by a+8d

a/q a+7d+a+8d=72

2a+15d=72

a=(72-15d)÷2-----------(1)

Now 4th term is given by
a+3d=-6
a=-6-3d-----------------(2)

FROM 1 AND 2 WE HAVE

=> -6-3d=(72-15d)÷2

=>-12-6d=72-15d

=>9d=84

=>d=84/9=28/3

Hence common difference is28/3

HOPE IT WILL BE CORRECT

PLZ MARK AS BRAINLIEST

Answer 2

thanks......................