If a2 - b2 = 10 and a*b = 5, find a4 + b4.  Choose one: A) 50 B) 100 C) 150 D) 92 E) 25

Rationale: a 2 - b 2 = 10 : given a 4 + b 4 - 2 a 2 b 2 = 102 : square both sides and expand . a * b = 5 : given a 2 b 2 = 52 : square both sides . a 4 + b 4 - 2 ( 25 ) = 100 : substitute a 4 + b 4 = 150 correct answer c
Answer: C