Step-by-step explanation:
Tn = a + (n-1)d
where a is the first term, d is the common difference and n is the nth term
For the 6th term: T6 = a + (6-1)d
= a + 5d
For the 8th term: T8 = a + (8-1)d
= a + 7d
From the question (a + 5d)/(a + 7d) = 7/9
From the Equation above, we can say that;
a + 5d = 7......1
a + 7d = 9.....2
Solving equations 1 & 2 simultaneously, we have that a = 2 and d = 1
Sn = n/2[2a + (n-1)d]
where Sn is the sum of nth terms, n is the nth term, a is the first term and d is the common difference.
By substituting the values gotten into this equation. You would be able to find the ration between the sum of the first 10 terms to the sum of the first 20 terms
