Latest TCS Aptitude Question SOLUTION: if A1=2,A(n+1)=An+2n, A100=?

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(#M40010651) TCS question TCS maths puzzle Keep an EYE

if A1=2,A(n+1)=An+2n,
A100=?

Asked In TCS vivek chauhan (11 years ago)

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SDeep Bhattacharya  (11 years ago)

A(n+1)=A(n)+2n
=>2n=A(n+1)-A(n)
=>2*1= A(2)-A(1)
=>2*2= A(3)-A(2)
=>2*3= A(4)-A(3)
=>2*4= A(5)-A(4)
=>2*5= A(6)-A(5)
.
.
.
.
.
.
.
.
=>2*98=A(99)-A(98)
=>2*99=A(100)-A(99)
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Summing up all the above terms we get,
2*(1+2+....+99) =A(100)-A(1)
=>A(100)={2*(1+99)*99}/2 + A(1)
=>A(100)=9900+2
=>A(100)=9902

Answer A(100)=9902

Is this solution Helpfull? Yes (48) | No   

subratverma  (11 years ago)

it forms g.p
so 100th term of gp =ar^(n-1)
first term =2
ratio=2
n=100
=2*2^(100-1)
=2^100
so a100 =2^100

Is this solution Helpfull? Yes (2) | No (16)  

palak purohit  (11 years ago)

MR. SDEEP, while suming all the terms using 2*(1+2+....+99) =A(100)-A(1), y hv u subtracted A1 ? from A(100) ? IN LHS.

Is this solution Helpfull? Yes (1) | No (2)  

Aditya Rao   (11 years ago)

when u try to solve the question ull notice tht the solution comes in form of ap
= 2*(99+98+97+96+95......1) +A(1)
=9902

Is this solution Helpfull? Yes | No (3)  

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