4x^4 - 45x^2 + 81 = 0
Пусть x^2 = t, тогда
4t^2 - 45t + 81 = 0
D = 45^2 - 4*81*4 = 729 = 27^2
t1 = ( 45 + 27)/8 = 72/8 = 9
t2 = (45 - 27)/8 = 18/8 = 2,25
Получим 2 случая
x^2 = 9
x = ± √9
x = ± 3
x^2 = 2,25
x = ± √ 2,25
x = ± 1,5
ОТВЕТ
- 3; - 1,5; 1,5; 3