for an arithmetic progression T7=18 ,T18=7, find T101
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Answer:
t₁₀₁ = -76
Step-by-step explanation:
t₇ = 18, t₁₈ = 7
tₙ = a + (n - 1)d
t₇ = a + 6d
t₁₈ = a + 17d
subtract t₇ and t₁₈
a + 6d - (a + 17d) = 18 - 7
a + 6d - a - 17d = 11
-11d = 11
∴d = -1
substitute d = -1 in t₇
t₇ = a + 6d
18 = a - 6
⇒ a = 18 + 6 = 24
a = 24
t₁₀₁ = a + 100d
= 24 + 100(-1)
= 24 - 100
t₁₀₁ = -76
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