Question

The sum of the third and seventh term of an A.P. is 8. Then
the sum of the first nine terms of this progression is?

Answer 1

Answer:

36

Step-by-step explanation:

A3+ A7=8 -------------(1)

S9=?

a=A1

a+(n-1)d=An

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

(1) gives,

a+2d+a+6d=8

2a+8d=8

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

S9=(9/2)(2a+8d)

S9=9(a+4d)

From (2),

S9=9*4=36