Question 30331
{{{ x^-4 -32 = 4x^-2 }}} and {{{ u+x^-2 }}}
What are we substituting u+x^-2 for?  What is it equal to?  I am going to assume that {{{ u+x^-2 }}} should actually be {{{ u=x^-2 }}}
First, set the first equation equal to 0
{{{ x^-4 -32 -4x^-2 = 0 }}} now ... the x^-4 needs to be rewritten
{{{ (x^-2)^2 -32 -4x^-2 = 0 }}} anywhere there is a x^-2 ... plug in a u
{{{ u^2 -32 -4u = 0 }}} put the equation in descending order
{{{ u^2-4u-32 = 0 }}}  the answer is b