1. x^4-81=0, x^4=81, x=3 2.125x^3+8=0; 125x^3=-8; x^3=-8/125; x^3=-0.064; x=0.4 3.16x^4-625=0; 16x^4=625; x^4=16/625; x^4=0.0256; x=0.4 4.125x^3-27=0; 125x^3=27; x^3=27/125; x^3=0.216; x=0.6