If The 6th term of an a.p -10 and its 10th term of the ap is -26, find the , fifteen term
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Answer:
Step-by-step explanation:
nth term of AP given by tₙ = a + (n - 1)d
6th term, t₆ = a + (6 - 1)d = -10
=> a + 5d = - 10 ---------------- (1)
10th term, t₁₀ = a + (10 - 1)d = -26
=> a + 9d = - 26 ---------------- (2)
Subtract (1) from (2),
a + 9d = - 26
a + 5d = - 10
- - +
--------------------
4d = - 16
=> d= - 4
Substitute value of d in (1),
a + 5d = - 10
=> a + 5(-4) = - 10
=> a = - 10 + 20 = 10
=> a = 10.
Thus 15th term, t₁₅ = 10 + (15 - 1) (- 4)
= 10 + 14 * - 4
= 10 - 96
= -86.
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