Question

Answer this question

Answer 1

here t1=2,t2=6

hence. d=6-2=4

Sn=n/2[2a+(n-1)d]

1800=n/2[4+(n-1)4]

1800=n/2 x 4[4(n-1)]

1800=2n[4(n-1)]

1800/4 x 2= n(n-1)

225=n²-n

n²-n-225=0

completing sq. method

n²-n+1/4-1/4-225=0

(n-1/2)²-1-900/4=0

(n-1/2)²-901/4=0

(n-1/2)²=901/4

sq.root

n-1/2=30/2

n=30/2+1/2

n=31/2

this is the approximate answer