Question

Дана ар. прогрессия -1,2,5.... найдите сумму первых пяти членов

Answer 1

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Answer 2

Arithmetic Progression and Sum of First Five Terms

The given arithmetic progression is -1, 2, 5. We need to find the sum of the first five terms.

Step 1: Find the Common Difference (d) The common difference (d) can be calculated using the formula: \[ d = a(2) - a(1) \]

Substitute the values: \[ d = 5 - 2 = 3 \]

Step 2: Find the Sum of the First Five Terms (S5) The sum of the first five terms can be calculated using the formula: \[ S5 = \frac{n}{2} \times (2a1 + (n-1)d) \]

Substitute the values: \[ S5 = \frac{5}{2} \times (2 \times 2 + (5-1) \times 3) = \frac{5}{2} \times (4 + 4 \times 3) = \frac{5}{2} \times 16 = 40 \]

Therefore, the sum of the first five terms of the given arithmetic progression -1, 2, 5 is 40.