Question 896525
Factor x^4-84 the same as x^2-y^2=(x-y)*(x+y)
It isn't as neat and pretty though
(x^2-2sqrt(21))*(x^2+2sqrt(21))
(x-sqrt(2)21^(1/4))*(x+sqrt(2)21^(1/4))*(x^2+2sqrt(21))


{{{(x^2-2sqrt(21))*(x^2+2sqrt(21))}}}
{{{(x-sqrt(2)21^(1/4))*(x+sqrt(2)21^(1/4))*(x^2+2sqrt(21))}}}