Find the AP in which the sum of the first 'n' terms is Sn=4n*n-3n

Asked by derrindarren | 22nd Dec, 2015, 09:55: PM

Expert Answer:

G i v e n space t h a t space s u m space o f space t h e space f i r s t space apostrophe n apostrophe space t e r m s space i s space S subscript n equals 4 n squared minus 3 n S u b s t i t u t i n g space n equals 1 comma space w e space h a v e comma space S subscript 1 equals 4 cross times 1 squared minus 3 cross times 1 equals 1 T h u s comma space t h e space i n i t i a l space t e r m comma space a equals 1 S u b s t i t u t i n g space n equals 2 comma space w e space h a v e comma space S subscript 2 equals 4 cross times 2 squared minus 3 cross times 2 equals 10 T h u s comma space t h e space s u m space o f space f i r s t space t w o space t e r m s equals 10 S i n c e space i n i t i a l space t e r m equals 1 space a n d space t h e space s u m space o f space f i r s t space t w o space t e r m s space i s space 10 comma space t h e space s e c o n d space t e r m equals 10 minus 1 equals 9 C o m m o n space d i f f e r e n c e equals S e c o n d space t e r m minus F i r s t space t e r m equals 9 minus 1 equals 8 T h u s comma space t h e space g i v e n space A P space i s space 1 comma space 9 comma space 17 comma space 25 comma space.... space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space

Answered by Vimala Ramamurthy | 23rd Dec, 2015, 11:06: AM