For how many unique pairs of nonnegative integers {a, b} is the equation a^2 - b^2 = 45 true?  Choices.
A) 1
B) 3
C) 5
D) 7
E) 9
Answer 3   (a+b)(a-b)=45   3cases For (a+b), (a-b)   45, 1   15, 3   9, 5   Answer 3
<result>B</result>
For how many unique pairs of nonnegative integers {a, b} is the equation a^2 - b^2 = 45 true?