Select all of the following for which there exist nonzero constants which can be substituted into the equation to make it true.
a) a/(x-2)(x+7)=b/(x-2)

b) a/(x-2)(x+7)=b/(x-2)+c/(x+7)

c) a/(x-2)(x+7)=b/(x-2)+c/(x+7)+6

d) none of the above?

The non zero constant is where if the both variables are substituted as zero the resulting would e non zero but also it should be valid and would make the equation true in the process of equality. I think the best answer to this question is D. none of the above