Question

if the 8th term of an AP is 15 then sum of first 15 terms is___

Answer 1

this is the solution and first term be a and difference d

Answer 2

Answer:

Step-by-step explanation:

aₙ =a+(n-1)d

there fore

a₈= a +7d = 15

sₙ = n/2 [ 2a+(n-1)d ]

there fore

s₁₅ = 15/2 [ 2a + 14d]

    = 15/2×2 [ a+7d]

    = 15 × 15

    = 225

if the 8th term of an AP is 15 then sum of first 15 terms is 225

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