If a2 - b2 =11 and a*b = 5, find a4 + b4.
Choose the correct choice from the following
A) 62 B) 181 C) 170 D) 171 E) 50
a2 - b2 = 11 : given   a4 + b4 - 2a2b2 = 112 : square both sides and expand.   a*b = 2 : given   a2b2 = 52 : square both sides.   a4 + b4 - 2(25) = 121 : substitute   a4 + b4 = 171   correct answer 171
<result>D</result>
If a2 - b2 =11 and a*b = 5, find a4 + b4.