Question

d=5,s9=75, find a & a9

Answer 1

Hii friend...........
common difference (d) = 5
S9 = 75
nth term (n) = 9
first term= ?
9th term= ?
so,Sn = n/2[2a+(n-1)d]
75 = 9/2[2a+(9-1)5]
75×2 = 9 [2a+(8)5]
150 = 9 [2a+40]
150 = 18a + 360
150-360 = 18a
-210 = 18a
a = -11.6

Then, a9 = a+8d
= -11.66+8×5
= -11.66+40
=28.4
Thanks
Hope it helps u☆☆