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Answer 1

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QUESTION :

The sum of first n term of an A.P is 3n² + 4n .Find the 25th term.

$OLUTION :

if we puts the value of n = 1

=> S1= 3n² + 4n

=> S1 = 3× (1)²+ 4×1

=>S1 = 3 +4

=> S1 = 7 .

if we put's the value of n = 2.

=> S2 = 3n² + 4n

=> S2 = 3× (2)² + 4 × 2

=> S2 = 3 × 4 + 4 × 2

=>S2 = 12 + 8

=> S2 = 20 .

then ,we know that ( S1 = a1 = 7 ).

=> now, a2 = S2 - S1

=> a2 = 20 - 7

=> a2 = 13.

now, we will find the common difference .

=> d = a2 - a1

=> d = 13 - 7

=> d = 6.

then , after getting all this values we will find the 25th term of A.p

=> we know that the formula =>

An = a + ( n - 1 ) × d

An = 7 + ( 25 - 1 ) × 6

=> 7 + 24 × 6

=> 7 + 144

=> 151

so, the AP of 25th term is 151

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Answer 2

Hii Mate....

The above given answer is correct.

hope this helps you !!