Question

find the sum of the aps. 2,7,12.......to10 terms
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Answer 1

$a = 2 \\ d = a2 - a1 \\ \: \: = 7 - 2 \\ \: \: = 5 \\ \\ a + (n - 1) d= an \\ \: \: 2 + (n - 1)5 = 10 \\ \: \: 2 + 5n - 5 = 10 \\ \: \: 5n - 5 = 10 - 2 \\ \: \: 5n - 5 = 8 \\ 5n = 8 + 5 \\ 5n = 15 \\ n = 3 \\ \\ sum = n \: upon \: 2(2a + (n - 1)d) \\ \\ = 3upon2(2 \times 2 + (3 - 1)5) \\ = 3upon2(4 + 2 \times 5) \\ = 3upon2 (4+ 10) \\ = 14 \times 2upon3 \\ = 28upon3 \\ = your \: answer \: is \: 28upon3 \\ \\ \\ i \: hope \: i \: help \: you \\ \\ \\ \\ \\ \\ thankyou \:$

Answer 2

Step-by-step explanation:

GIVEN

• a = 2
• d = 5
• n = 10

We Know That

Sₙ = n/2 [ 2a + (n -1)d ]

• Put the given value

Sₙ = 10/2 [ 2*2 + (10 -1)5 ]

Sₙ = 5 [ 4 + 45 ]

Sₙ = 5 * 49

Sₙ = 245