यदि किसीA.P.के प्रथम 7 पदों का योग 49 है और प्रधम 17 पदों का योग 289 है, तो इसके प्रथम n पदों का योग ज्ञात कीजिए
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Step-by-step explanation:
7/2 {2a + 6d} = 49
7(a+3d) = 49
a+3d = 7
A(4) = 7
17/2 {2a+16d} = 289
17(a+8d) = 289
a+8d = 17
a+3d = 7
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5d = 10 , d = 2
a = 7-3(2) = 7-6 = 1
S(n) = n/2 {2(1) + (n-1)2}
= n/2 {2 + 2n - 2}
= n/2 * 2n = n*n = n²
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