What is the best to solve the question of arithmetic progressions of exercise 5.3 of math. Please help me for solving this problem Find the sums given below
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First term, a = 7
nth term, an = 84
Let 84 be the nth term of this A.P., then as per the nth term formula,
an = a(n-1)d
84 = 7+(n – 1)×7/2
77 = (n-1)×7/2
22 = n−1
n = 23
We know that, sum of n term is;
Sn = n/2 (a + l) , l = 84
Sn = 23/2 (7+84)
Sn = (23×91/2) = 2093/2