If a2 - b2 =11 and a*b = 5, find a4 + b4.
Choices:
A) 62	B) 181	C) 170	D) 171	E) 50

Rationale: "a 2 - b 2 = 11 : given a 4 + b 4 - 2 a 2 b 2 = 112 : square both sides and expand . a * b = 2 : given a 2 b 2 = 52 : square both sides . a 4 + b 4 - 2 ( 25 ) = 121 : substitute a 4 + b 4 = 171 correct answer d"
Answer: D