Question

write an A.P those first term is a and the common difference d.
1.
$a = - 5 \: \: \: d = - \frac {1}{3}$
2.
$a = 20 \: \: d = \sqrt{3}$

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Answer 1

Answer:

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Answer 2

Answer:

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Step-by-step explanation:

the value of an is 11

the sum of first n terms of AP is

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

where, a is first term and d is common difference.

It is given that the first term is 8 it and the the common difference is 20. the sum of n terms is

Sn=n/2{2(8)+(n-1)20}

Sn=n/2 {16+20n-20}

Sn=n/2{20n-4}

Sn=n(10n-2)

the first term of another A.P is -30 and common difference is 8 the sum of 2n terms is

S2n =2n/2 {2(-30)+(2n-1)8}

S2n =n(-60+16n-8)

S2n =n(16n-68)

it is given that sum of n terms of another A.P

n(10n-2)=n(16n-68)

10n-2=16n-68

-2+68=16n-10n

66=6n

11=n

therefore the value of n is 11

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