Question

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

Answer 1

$x^{4} = (x-20)^{2} \\ x^{4} -(x-20)^{2} = 0 \\ (x^{2} -(x-20))(x^{2}+(x-20)) = 0 \\ (x^{2} - x+20)(x^{2}+x-20) = 0$
$x^{2} - x+20=0$   или   $x^{2}+x-20= 0$

Первое:
$x^{2} - x+20=0 \\ D= 1 - 4*20 < 0$   нет решений

Второе:
$x^{2}+x-20= 0 \\ x_{1}+ x_{1} = -1 \\ x_{1} x_{1} = -20 \\ x_{1}= -5, x_{1}= 4$

Ответ:  -5 ; 4.

Answer 2

(x²)²-(x-20)²=0
(x²-x+20)(x²+x-20)=0
(x²-x+20)(x+5)(x-4)=0
x₁=-5  x₂=4
Ответ: x₁=-5  x₂=4