Question

the sum of third and seventh term of an ap is 6 and their product is 8 FInd the sum of 20 terms of the AP

Answer 1

here is ur answer............
third term=a+2d
7th term=a+6d
so acc. to ques.
a+2d+a+6d=6
2a+8d=6
a+4d=3
a=3-4d...........1.
(a+2d)(a+6d)=8
put value of a from one equation..
(3-4d+2d)(3-4d+6d)=8
(3-2d)(3+2d)=8
9-4d^2=8
-4d^2=8-9
d=1/2..
so a=1
so , the sum of 20 terms is=n/2(2a+(n-1)d)
                                           =10(2+19*1/2)
                                           =115
hope this helps uh.............