Question

sqrt(2){x}-2sqrt(4){x}-15=0

Answer 1

$sqrt{x} -2 sqrt[4]{x} -15=0;quad x geq 0\\ t=sqrt[4]{x} ;quad t geq 0 \t^2-2t-15=0\t_1=-3 textless 0;quad t_2=5\\5= sqrt[4]{x} quadRightarrowquad x=5^4=625$