The roots of \(\displaystyle{x}^{{3}}+{4}{x}-{1}={0}\) are a,b,c. Find

Haylee Bowen

Haylee Bowen

Answered question

2022-04-11

The roots of x3+4x1=0 are a,b,c.
Find (a+1)3+(b+1)3+(c+1)3

Answer & Explanation

webhui2v2

webhui2v2

Beginner2022-04-12Added 10 answers

Let the equation
6y37y2+3y1=0 (*)
have roots α,β and γ
Using Vieta's formulas:
α=α+β+γ=76=76 (1)
αβ=αβ+βγ+γα=36=12
Using the identity α2=(α)22αβ gives
α2=49362×12=1336
Rearranging (*)
6y3=7y23y+1
so that
6(α3)=7(α2)3(α)+1+1+1
(after adding 6β3=7β23β+1, 6β3=7β23β+1 and 6γ3=7γ23γ+1)
Applying (1) and (2)
α3=16(7×13363×76+3)=73216

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