Question

find the 60thterm of the ap 8 ,10,12,...if it has terms and Hance find the sum of its last 10 terms​

Answer 1

Step-by-step explanation:

Ap. series- 8,10,12

a=8

d=a2-a1

d=10-8

d =2

T60=a+(n-1)d

=8+(60-1)2

=8+59×2

= 8+118

T10=126

Sn= n/2[2a+(n-1)d]

126=n/2[16+(n-1)2]

126/2=n[16+2n-2]

63 =n[14+2n]

63=14n+2n^2

2n^2-14n-63=0

2n^2-7n-7n-63=0

2n(n-7)-9(n-7)=0

(2n-9) (n-7)=0

n-7=0, 2n-9=0

[n=7] , n=9/2(wrong)

answer =(n=7).

hence proved.