Question

Find the sum of the AP: 2,7,12 to 10 terms.​

Answer 1

Clearly, the given sequence is an AP with first term a=2, common difference d=5 and n=10.

Now,

s10 = 10/2 (2a + 10-1d)
=5(2x2+9x5)

=245

Explanation:

Answer 2

S₁₀ = 245

Explanation:

the sum to n terms of an AP is

`S_(n)` =
`(n)/(2)` [ 2a₁ + (n - 1)d ]

where a₁ is the first term and d the common difference

here a₁ = 2 and d = a₂ - a₁ = 7 - 2 = 5 , then

S₁₀ =
`(10)/(2)` [ (2 × 2) + (9 × 5) ]

= 5(4 + 45)

= 5 × 49

= 245