Question

given a=2 ,d=8, Sn=90, find a= ? and A9​

Answer 1

Step-by-step explanation:

Here,

Given :

a = 2

d = 8

sn = 90

So,

According to formula ,

Sn = a + ( 2d - a)d = A9

90 = 2 + ( 16 - 2) 8

90 = 2 + 128 - 16

90 = 130 -16

90A9= 114

A9 = 114/90

Answer 2

Step-by-step explanation:

Sn = n + a+ ( n - 1)d

2

90 = 2 + a + (2 - 1)8

2

90=1 + a + 8

90=a+9

or a+9=90

a=90-9

a=82

A9=a+(n-1)d

=82+(2-1)8

=82+8

=90