Question

If T15=9 and T9=15, then d= ​

Answer 1

Step-by-step explanation:

t15=9,

a+14d=9. equation 1

t9=15

a+8d=15. equation 2

Now,

equation 2-equation 1

a-a+8d-14d=15-9

-6d =6

d=6/-6

d=-1