f(x)=18x3−33x2+20x−4=0 α is a repeated root of multiplicity ? Let roots be α,α,βf′(x)=54x2−66x+20x=α is repeated roots, f′(α)=0 and 54α2−66α+20=0 ‌⇒‌‌27α2−33α+10=0 ‌⇒‌‌27α2−18α−15α+10=0 ‌⇒‌‌(9α−5)(3α−2)=0⇒α=‌