0, The equation formed by decreasing each root of the equation ` a x^2 + bx + c = 0` by 1 is ` 2 x^2 + 8x + 2 = 0` then

Explanation

Let `alpha,beta ` are the roots of equation `ax^2+bc+c = 0`

Then, `alpha-1` and `beta-1` are the roots of equation `2x^2+8x+2 = 0`

Then, sum of roots, ` (alpha-1)+(beta-1) = -8/2`

`=>alpha+beta = -4+2`

`=>alpha+beta = -2->(1)`

Product of roots, ` (alpha-1)(beta-1) = 2/2`

`=>alphabeta-alpha-beta+1 = 1`

`=>alphabeta -(alpha+beta) = 0`

...