Answer:
see explanation
Step-by-step explanation:
The nth term of an AP is
 = a₁ + (n - 1)d
 = a₁ + (n - 1)d
where a₁ is the first term and d the common difference
Given a₅ is double a₇ , then
a₁ + 4d = 2(a₁ + 6d) , that is
a₁ + 4d = 2a₁ + 12d ( subtract a₁ from both sides )
4d = a₁ + 12d ( subtract 12d from both sides )
- 8d = a₁
The sum of n terms of an AP is
 =
 =  [ 2a₁ + (n - 1)d ] , substitute values
 [ 2a₁ + (n - 1)d ] , substitute values
 =
 =  ( 2(- 8d) + 16d)
 ( 2(- 8d) + 16d)
      = 8.5(- 16d + 16d)
      = 8.5 × 0
      = 0