Question

If sn=4n-n2 find it's 11th term​

Answer 1

Step-by-step explanation:

Sn=4n-n²

n(2a+(n-1)d)=n(4-n)

2

2a+(n-1)d=8-n

2a-d+nd=8-n

nd= -n. 2a-d=8

d= -1 2a+1=8

2a=7

a=7/2

Tn=a+(n-1)d

T11=7/2+(11-1)(-1)

=7/2-10

= -13/2