Question

If the 3rd and 9th term of AP are 4 and -8 which term of this AP is zero?

Answer 1

The Nth term of an AP = a+(n-1)d

3rd term= 4 , 9th term= -8

4 = a+3d-3       -8=a+9d-3

7= a+3d            -5=a+9d

multiply 7=a+3d by 3 to get 21= 3a+9d

subtract the two equations

3a+9d=21 and a+9d= -5 t get

2a= 26 ==> a = 13 ( substitute this value in any of the established equations)

7=13+3d

-6=3d

d=-2

Now that we have both the first term and the common difference, all we need to do is substitute it in the given problem (i.e, 0=a+(n-1)d)

Answer 2

Answer:

Please refer the attachment dear