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CBSE Class 10 Answered

the sum of the first n terms of an AP is 4n^2 +5n. find the AP
Asked by fernandeschristine01 | 06 Dec, 2017, 10:36: AM
answered-by-expert Expert Answer
begin mathsize 16px style Sum space of space first space straight n space terms space of space an space straight A. straight P. equals 4 straight n squared plus 5 straight n rightwards double arrow straight S subscript 1 equals 4 left parenthesis 1 right parenthesis squared plus 5 left parenthesis 1 right parenthesis equals 4 plus 5 equals 9 equals straight a equals straight t subscript 1 straight S subscript 2 equals 4 left parenthesis 2 right parenthesis squared plus 5 left parenthesis 2 right parenthesis equals 16 plus 10 equals 26 rightwards double arrow straight t subscript 1 plus straight t subscript 2 equals 26 rightwards double arrow 9 plus straight t subscript 2 equals 26 rightwards double arrow straight t subscript 2 equals 17 Now comma space straight t subscript 2 minus straight t subscript 1 equals 17 minus 9 equals 8 equals straight d Thus comma space required space straight A. straight P. equals straight a comma space straight a plus straight d comma space straight a plus 2 straight d comma....... equals 9 comma space 17 comma space 26 comma space 35 comma......... end style
Answered by Rashmi Khot | 06 Dec, 2017, 11:35: AM

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CBSE 10 - Maths
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