If a and b are positive integers and (a-1)(b+1)=0 , which of the following must be true?

A)a>b

B)a<b

C)a=b

D)a=1

E)b=1do you have any tips on how to deal with this type of question?

To get this one, you need to read super carefully. For that equation to be true, either *a* – 1 = 0, or *b* + 1 = 0 (or both). However, since **the question says a and b are positive integers**,

*b*+ 1

*cannot*be zero. Therefore,

*a*– 1 must be zero, which means

*a*must equal 1.