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CBSE Class 11-science Answered

sir can give me answer for this question
Asked by ramhari | 27 Apr, 2010, 02:28: PM
Expert Answer

Dear Student,

Let us examine the 1st terms of each row.

1st row........1

2nd row.......3 ..........(1+2.1)

3rd row.......7............(1+2.1+2.2)

4th row......13..........(1+2.1+2.2+2.3)

.

.

nth row..................(1+2.1+2.2+2.3+........+2.(n-1))

Hence. 1st element of nth row is:

(1+2.(1+2+3+......+n)-2n)

=>(1+2.n(n+1)/2-2n)

=>(n2-n+1).

Similarly, analysing the last terms of each row:

1st row........1

2nd row.......5 ..........(1+2.2)

3rd row.......11............(1+2.2+2.3)

4th row......19..........(1+2.2+2.3+2.4)

.

.

nth row.................(1+2.2+2.3+2.4+..........+2.n)

=>(1+2.(1+2+3+4+.....+n)-2)

=>(1+2.n.(n+1)/2-2)

=>The last term of nth row is (n2+n-1).

By inspection, for n= 45, first tem is1981, and last term is 2069 (within which 2009 is lying).

Regards Topperlearning.

Answered by | 26 May, 2010, 09:43: PM
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