Question 57546
It seems that you tried to factor out X^2 from X^4 - 20X^2 + 64=0
However to do this X^2 has to be included in all the terms ie 64X^2.
The difference of squares method can be applied to this equation.
X^4 - 20X^2 + 64= (X^2-16)(X^2-4)=0
X^2=16 X=+/-4
X^2=4 X=+/-2
Sollution set is (-4, -2, 2, 4)