For how many unique pairs of nonnegative integers {a, b} is the equation a^2 - b^2 = 25 true?  Choose one: A) 1 B) 3 C) 5 D) 2 E) 9

Rationale: answer d ( a + b ) ( a - b ) = 25 5 cases for ( a + b ) , ( a - b ) 25 , 1 5 , 5 answer d
Answer: D