Question

if 12th term of ap is -13 and sum of first 4 terms is 24 find sum of first 10 terms

Answer 1

Hi,

Let a and b are first term and

common difference of an A P.

n th term = tn = a+ ( n - 1 ) d

i) given t12 = - 13

a + 11d = -13 ---------(1)

ii) sum of first 4 terms = 24

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Sn = n/2 [ 2a + ( n-1 ) d ]
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S4 = 24

4/2 [ 2a + 3d] = 24

2[2a + 3d ] = 24

2a + 3d = 12 ------------(2 )

Multiply equation ( 1 ) with 2 and

subtract from (2)

We get

-19 d = 38

d = -2
Put d value in (1)

a - 22 = -13

a = -13 + 22

a = 9

iii) a = 9 , d = -2 , n =10

S 10 = 10/2 [ 2 × 9 + ( 10 - 1 ) ( - 2 ) ]

= 5 [ 18 - 18 ]

= 5 × 0

= 0

Therefore,

Sum of first 10 terms = S 10 = 0

I hope this will useful to you.

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Answer 2

please mark it as brainist