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समांतर श्रेणी

Question
CBSEHHIMAH10010267

8 के प्रथम 15 गुणजों का योग ज्ञात कीजिए।

Solution

8 के गुणज हैं: 8, 16, 24, 32, ... जो की एक A.P. बनाते है।
यहाँ,  a = 8, d = 16 – 8 = 8, n = 15
straight S subscript straight n space equals space straight n over 2 space left square bracket space 2 straight a space plus left parenthesis straight n space minus space 1 right parenthesis space straight d space right square bracket
rightwards double arrow space straight S subscript straight n space equals space 15 over 2 space left square bracket space 2 space cross times space 8 space plus space left parenthesis 15 space minus space 1 right parenthesis space cross times space 8 space right square bracket
equals space 15 over 2 space left square bracket space 16 space plus space 14 space cross times space 8 space right square bracket
equals space 15 over 2 space left square bracket space 16 space plus space 112 space right square bracket
equals space 15 over 2 space cross times space 128 space equals space 15 space cross times space 64 space equals space 960
8 के प्रथम 15 गुणजों का योग = 960