b: Đặt \(\sqrt[3]{x^4-1}=a\)
=>a^3+a-2=0
=>a=1
=>x^4-1=1
=>x^4=2
=>\(x=\pm\sqrt[4]{2}\)
c: =>\(\sqrt[3]{x^2-4x+31}=-x^2+4x-1=-\left(x^2-4x+1\right)=-\left(x^2-4x+31-30\right)\)
=>\(\sqrt[3]{x^2-4x+31}=-\left(x^2-4x+31\right)+30\)
Đặt \(\sqrt[3]{x^2-4x+31}=a\)
=>a=-a^3+30
=>a=3
=>x^2-4x+31=27
=>x=2