If a - b = 10 and a2 + b2 = 210, find the value of ab.	Choices
A) 68
B) 42
C) 55
D) 18
E) 44

Rationale: "2 ab = ( a 2 + b 2 ) - ( a - b ) 2 = 210 - 100 = 110 ab = 55 . answer : c"
Answer: C