X⁴ = (2x -15)²⇔ (x²)² =(2x -15)² ⇔(x²)² - (2x -15)² =0 * * * a² - b² =(a-b)(a+b) * *
(x²- (2x-15) )* (x²+ 2x-15) =0 ⇔ (x²-2x+15) (x²+ 2x-15) =0 . ⇔
⇔[ (x -1)²+14=0 ; x²+ 2x -15 =0. ⇔ [ x ∈∅ ; x² + 2x -15 = 0 .
x²-2x-15=0 ; D/4 =1² -(-15) =16 = 4²
x₁ =1- 4 = - 3 ;
x₂ =1+4 = 5.
ответ : { - 3 ; 5} .