Page 14 - Math Grade 11 (Advance)

PROEUS DARA

4.

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~n (a ) 3 7 13 21 31 ...
11
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tJ bli hltl n'&S hlnHl13d ru§Hti~ n ru sl ~~
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l
a - a = 3 - 1 = 2 x 1
2 1
a - a = 7 - 3 = 4 = 2 X 2
3 2
a -a = 13-7 = 6 = 2x3
4
3
__ -an
a 11 1 2 =2X(n 2)
an-an-I= 2x(n-l)

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U 1'1 A
a - a =an- 1 = 2 X 1 + 2 x 2 + 2 X 3 + ... + 2 X (n- 2) + 2 x (n....: 1)
11 1
a = 2Xl+2X2+2X3+ ... +2x(n-2)+2x(n-l)+l
11
= 2x[ 1+2+3+ ... +(n-2)+(n-l)]+l = 2x[ l+(n- l)](n-l)+l
2
2
= n(n- 1) + 1 = n - n + 1

9