Question

Fimd the 60th term of ap 8,10,12,..,fi it has a total of 60 terms and hence find the sum of its last 10 term

Answer 1

AP: 8, 10, 12, .... , t60 hey
a = 8, d = 2, n = 60
an = a + (n-1)d
a60 = 8 + (59)2
a60 = 8 + 118
a60 = 126
therefore AP is 8, 10, 12, .... , 126
considering the reverse order:
AP will be 126, 124, 122, .... , 8
where a = 126, d = -2, an = 8, n = 60
Sn = (2a + (n-1)d)n/2
S10 = (2*126 + 9*-2)5
S10 = (252 - 18)5
S10 = 234*5
S10 = 1170

therefore the 60th term is 126 and sum of last 10 terms is 1170.