If the sum of the 8th and the 9th of an a.p is 72 and the 4th term is -6 .find the common difference
Please solve
you know, making a second post saying "please solve" isn't really necessary. We assume that when you post a math problem, you want it solved!!
So, it's been an hour -- have you solved it yet? If not, start with
a+7d + a+8d = 72
a+3d = -6
now solve those as usual.