Answer :
The sum of the first 75 terms of the arithmetic sequence that has 10th term as 16 and the 35th term as 66 is 5400.
How to find the sum of terms using Arithmetic sequence formula
aₙ = a + (n - 1)d
where
- a = first term
- d = common difference
- n = number of terms
Therefore, let's find a and d
a₁₀ = a + (10 - 1)d
a₃₅ = a + (35 - 1)d
Hence,
16 = a + 9d
66 = a + 34d
25d = 50
d = 50 / 25
d = 2
16 - 9(2) = a
a = 16 - 18
a = -2
Therefore, let's find the sum of 75 terms of the arithmetic sequence
Sₙ = n / 2 (2a + (n - 1)d)
S₇₅ = 75 / 2 (2(-2) + (75 - 1)2)
S₇₅ = 37.5 (-4 + 148)
S₇₅ = 37.5(144)
S₇₅ = 5400
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