If the sum of 8th and 9th terms of an AP Is 72 and the 4th is -6,find the common difference
2 answers
No idea
a+7d + a+8d = 72
2a + 15d = 72, #1
a + 3d = -6 or 2a + 6d = -12, #2
#1 - #2 ====> 9d = 84
d = 84/9 = 28/3
2a + 15d = 72, #1
a + 3d = -6 or 2a + 6d = -12, #2
#1 - #2 ====> 9d = 84
d = 84/9 = 28/3