Question

Find sum of the 9th term of AP is 5 10 15

Answer 1

Answer:

Sum of first 9 terms of the arithmetic sequence = 225

Step-by-step explanation:

Arithmetic sequence = 5, 10, 15, 20...

Common difference (d) = x₂ - x₁ (second term - first term)

= 10 - 5 = 5

x₉ = x₁ + 8d = 5 + 8 × 5 = 40 + 5 = 45

Sum of first 9 terms of the arithmetic sequence = 1/2n(x₁ + x₉)  

= 1/2 × 9 ( 5 + 45)

= 9/2 × 50

= 9 × 25

= 225

∴ The sum of first 9 terms of the arithmetic sequence 5, 10, 15... is 225.

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