If a2 - b2 = 8 and a*b = 2, find a4 + b4. Choose the correct option: A) 62 B) 72 C) 82 D) 92 E) 62
a2 - b2 = 8 : given   a4 + b4 - 2a2b2 = 82 : square both sides and expand.   a*b = 2 : given   a2b2 = 22 : square both sides.   a4 + b4 - 2(4) = 82 : substitute   a4 + b4 = 72   correct answer 72
<result>B</result>
If a2 - b2 = 8 and a*b = 2, find a4 + b4.