Question

Find the sum of first 25 terms of the Ap-1, 2, 5, 8.11​

Answer 1

Answer:

74+59

Step-by-step explanation:

• ✓n = 20
• ✓n = 25

so, sum of the terms are

• a25 + a20
• 74 + 59

Answer 2

Required Answer :

The sum of first 25 terms of A.P. = 875

Given :

• Arithmetic progression = - 1, 2, 5, 8, 11

To find :

• The sum of first 25 terms

Knowledge Required :

Formula to calculate the common difference :-

• D = t₂ - t₁

where,

• D denotes the common difference
• t₁ denotes the first term
• t₂ denotes the second term

Formula to calculate the sum of terms :-

• Sum = n/2 [2a + (n - 1)d]

where,

• n denotes the number of terms
• a denotes the first term

Solution :

Common difference :

→ D = t₂ - t₁

we have,

• t₂ = 2
• t₁ = - 1

→ Common difference = 2 - (-1)

→ Common difference = 2 + 1

→ Common difference = 3

Sum of first 25 terms :

→ S = n/2 [2a + (n - 1)d]

we have,

• n = 25
• a = - 1
• d = 3

→ Sum = 25/2 [2(-1) + (25 - 1)3)]

→ Sum = 25/2 [-2 + (24)3]

→ Sum = 25/2 [ -2 + 72]

→ Sum = 25/2 [70]

→ Sum = 25/2 × 70

→ Sum = 25 × 35

→ Sum = 875

Therefore, the sum of first 25 terms of A.P. = 875