Question

For the sequence 2, 5, 8 find the sum of the first 15 terms

Answer 1

The sum of first 15 terms is 345

Step-by-step explanation:

GIVEN

a = t₁ = 2

t₂ = 5

t₃ = 8

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TO FIND

The sum of first 15 terms

___________________________

We know that,

Common Difference ( D ) = t₂ - t₁

Common Difference ( D ) = 5 - 2

Common Difference ( D ) = 3

Common Difference ( D ) is 3

___________________________

We know that,

Sn = n/2 × ( 2a + ( n - 1 ) × d )

S₁₅ = 15/2 × ( 2 × 2 + ( 15 - 1 ) × 3 )

S₁₅ = 15/2 × ( 4 + 14 × 3 )

S₁₅ = 15/2 × ( 4 + 14 × 3 )

S₁₅ = 15/2 × ( 4 + 42 )

S₁₅ = 15/2 × 46

S₁₅ = 7.5 × 46

S₁₅ = 345

The sum of first 15 terms is 345