Question

An arithmetic progression 5 12 19 has 50 terms find its last term and sum of its last 15 terms

Answer 1

HELLO......!
Above is your answer....
Last term is 348
sum of last 15 terms is 4485



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Answer 2

Answer:

Step-by-step explanation:

Solution :-

We have, a = 5, d = 12 - 5 = 7

and n = 50

We know that,

a(n) = a + (n - 1)d

a(50) = 5 + (50 - 1)7

= 5 + 49 × 7

= 348

Also the first term of the A.P. of last 15 terms be a(36)

a(36) = 5 + (36 - 1)7

= 5 + 35 × 7

= 5 + 245

= 250

Now, sum of last 15 terms,

S(n) = n/2[2a + (n - 1)d]

⇒ S(n) = 15/2[a × 250 + (15 - 1)7]

⇒ S(n) = 15/2[500 + 14 × 7]

⇒ S(n) = 15/2 × 598

⇒ S(n) = 4485

Hence, the sum of last 15 terms is 4485.

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