The 4th term of an AP is 6. If the sum of the 8th and 9th terms is -72, the com. mon difference is:

Question

asked Nov 1, 2022 199k views

1 Answer

ZSkycat · Answer 1 · 2022-11-07T04:13:42+0000

Answer:

t(4) = 6 ---- a + 3d = 6

t(8) + t(9) = -72

a+7d + a+8d = -72

2a + 15d = -72

double the first equation

2a + 6d = 12

subtract them

9d = -84

d = -84/9 = -28/3

Explanation: