Question

$x^{4} =(x-20) ^{2}$

Answer 1

$x^{4} =(x-20) ^{2} \\ sqrt{x^{4}} =sqrt{(x-20) ^{2} }\ \|x^2|=|x-20|\\x^2=|x-20|\\1)x geq 20\\x^2=x-20\\x^2-x+20=0\\D=1-80<0\ \ 2) x<20\ x^2=-x+20\x^2+x-20=0\D=1+80=81\\x_1= frac{-1+9}{2} =4;quad x_1= frac{-1-9}{2} =-5$