If x^2+(1/x^2)=9, x^4+(1/x^4)=?  Pick one:
A) 10
B) 11
C) 12
D) 14
E) 79
-&gt; x^4+(1/x^4)=(x^2)^2+(1/x^2)^2=(x^2+1/x^2)^2-2x^2(1/x^2)=9^2-2=79.   Thus, the answer is 79.
<result>E</result>
If x^2+(1/x^2)=9, x^4+(1/x^4)=?