Given,
x6−x−12=x−21⇒x(x−1)6(x−1)−2x=x−21⇒x2−x6x−6−2x=x−21⇒x2−x4x−6=x−21⇒(4x−6)(x−2)=x2−x⇒(4x2−8x−6x+12)=x2−x⇒4x2−x2−14x+x+12=0⇒3x2−13x+12=0⇒3x2−9x−4x+12=0⇒3x(x−3)−4(x−3)=0⇒(3x−4)(x−3)=0⇒3x−4=0 or x−3=0x=34 or x=3.
Hence, roots of given equation are 3,34