Question

How many terms of an AS 17+15+13.... are needed to sum 80

Answer 1

Answer:

Step-by-step explanation:

80=n/2 (34+(n-1)×2)

80=n/2 (34+2n-2)

80=34n+2n^2-2n/2

160=32n+2n^2

2n^2+32n-160=0

2n^2+40n-8n-160=0

2n (n+20)-8 (n+20)=0

(n+20)(2n-8)=0

n=4 Ans