Question

find the A.P Given a=2,d=8,Sn=90 find n and an​

Answer 1

Step-by-step explanation:

a=2 d=8 Sn=90

Sn=n/2{2a+(n-1)d}

=>90=n/2{2×2+(n-1)8}

=>90=n/2(4+8n-8)

=>180=n(8n-4)

=>8n^2-4n-180=0

=>2n^2-n-45=0

=>2n^2-10n+9n-45=0

=>2n(n-5)+9(n-5)=0

=>(n-5)(2n+9)=0

n=5 2n+9=0

=>2n= -9

=>n= -9/2

Answer 2

$\huge\tt\colorbox{lightblue}{Answer}$

n = 5

an = 34