Let f(x)=x4−2x3+6x−21=0 Required equation where roots are squares of the roots of f(x) is f(√x)=0 ‌(√x)4−2(√x)3+6√x−21=0 ⇒‌‌x2−2x√x+6√x−21=0 ⇒‌‌x2−21=2x√x−6√x ⇒‌‌x2−21=2√x(x−3) ⇒‌‌(x2−21)2=4x(x−3)2 ⇒‌‌x4−42x2+441=4x(x2−6x+9) ⇒‌‌x4−42x2+441=4x3−24x2+36x ⇒‌‌x4−4x3−18x2−36x+441=0