Question

solve x^4-25x^2+144=0

Answer 1

$x^4-25x^2+144=0 \ x^2=t \ t^2-25t+144=0 \ D=25^2-4*144*1=49 \ t_{1,2} = frac{25+/-7}{2} \ t_1 = 16 ; t_2=9 ; \ x^2=16 ; x = +-4 ; x^2=9 ; x = +-3$