Question

The 2nd and 12th term of an ap are 14 and 18 respectively ,find the sum of 51st term of an al

Answer 1

Explanation:

Given

a2 = 14

which mean = a +(n-1)d = a+ d = 14 __ (1)

and ,

a12 = 18

same as = a+11d = 18 ____(2)

solving eq 1& 2

a+d = 14

a +11d = 18

we get

a= 68/5

d = 2/5

now according to question

the sum of 1st 51 th term

as we know that

Sn = n/2 ( 2a + (n-1)d )

S51 = 51/2 (2×68/5 + (51-1)× 2/5

S51= 25.5 ( 136/5 + 50 × 2/5)

S51 = 25.5 ( 27.2 + 20)

S51 = 25.5 (47.2)

S51 = 1203.6

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Answer 2

Sum of 51st term = 1203.6

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