Answer :
To rewrite the equation
[tex]$$4x^4 - 21x^2 + 20 = 0$$[/tex]
as a quadratic equation, you can make the substitution
[tex]$$u = x^2.$$[/tex]
Notice that with this substitution, we have
[tex]$$x^4 = (x^2)^2 = u^2.$$[/tex]
Substituting into the equation gives
[tex]$$4u^2 - 21u + 20 = 0.$$[/tex]
This is now a quadratic equation in terms of [tex]$u$[/tex]. Thus, the correct substitution is
[tex]$$u = x^2.$$[/tex]
[tex]$$4x^4 - 21x^2 + 20 = 0$$[/tex]
as a quadratic equation, you can make the substitution
[tex]$$u = x^2.$$[/tex]
Notice that with this substitution, we have
[tex]$$x^4 = (x^2)^2 = u^2.$$[/tex]
Substituting into the equation gives
[tex]$$4u^2 - 21u + 20 = 0.$$[/tex]
This is now a quadratic equation in terms of [tex]$u$[/tex]. Thus, the correct substitution is
[tex]$$u = x^2.$$[/tex]
