Question

if x3 + 1/x 3 = 10, than x+1/x=​

Answer 1

☆ 5

▪︎ (x+x1)3=(x3+x31)+3(x+x1)

⇒  (x+x1)3=110+3(x+x1)

Let y=x+x1

⇒  y3=110+3y

⇒  y3−3y−110=0

⇒  y3−5y2+5y2−3y−110=0

⇒  y2(y−5)+5y2−25y+22y−110=0

⇒  y2(y−5)+5y(y−5)+22(y−5)=0

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