CBSEi Class 10 Sequences (AP and GP) CORE
CBSEi Class 10 Sequences (AP and GP) CORE
CBSEi Class 10 Sequences (AP and GP) CORE
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Example 23: find the sum of first<br />
(i) <strong>10</strong>0 natural numbers.<br />
(ii) <strong>10</strong>00 natural numbers.<br />
Solution: (i) Here a=1, d=1, n = <strong>10</strong>0<br />
Thus, S<strong>10</strong>0 = [2x1 + (<strong>10</strong>0-1) 1] = 50x <strong>10</strong>1 = 5050<br />
Alternatively, we may use the formula<br />
Sn = (a + )<br />
S<strong>10</strong>0 = (1+<strong>10</strong>0) = 5050<br />
(ii) Using the formula for Sn,<br />
S<strong>10</strong>00 = [2 x 1 + (<strong>10</strong>00 1 1]<br />
= 500 (<strong>10</strong>01)<br />
= 500500<br />
Also by using the formula :<br />
Sn = (a+ )<br />
S<strong>10</strong>00 = (1 + <strong>10</strong>00)<br />
= 500 (<strong>10</strong>01)<br />
= 500500<br />
Example 24: Find the sum of first 50 terms of the <strong>AP</strong>; 1, 3, 5, 7,………..<br />
Solution: Here a=1, d=2, n=50<br />
using the formula<br />
62