If the sum of first n terms of AP is 6n-n^2 find its 25th term

Asked by lovemaan5500 | 13th Dec, 2017, 06:13: PM

Expert Answer:

begin mathsize 16px style straight S subscript 1 equals 6 minus 1 equals 5
straight S subscript 2 equals 6 cross times 2 minus 2 squared equals 8
straight t subscript 2 equals straight S subscript 2 minus straight S subscript 1
straight t subscript 2 equals 3
straight a equals straight S subscript 1 equals 5
straight d equals straight t subscript 2 space end subscript minus space straight a
straight d equals 3 space minus space 5 space
straight d space equals space minus 2
Find space 25 to the power of th space term comma
straight t subscript 25 equals straight a plus left parenthesis straight n minus 1 right parenthesis straight d
equals 5 plus 24 cross times open parentheses negative 2 close parentheses
equals negative 43 space end style

Answered by Sneha shidid | 13th Dec, 2017, 07:00: PM