Let α,β,γ be the three roots of the equation x3+bx+c=0. If βγ=1−α, then b3+2c3−3α3−6β3−8γ3 is equal to
Explanation
Given cubic equation is :
x3+bx+c=0
∴ α,β,γ are the roots of above equation.
And βγ=1=−a
So, product of roots =−c
⇒αβγ=−c
⇒(−1)(1)=−c
⇒c=1
Since, α=−1 is the root. So,
⇒−1−b+c=0
⇒c−b=1
⇒1−b=1⇒b=0
The given equation becomes x3+1=0
So, roots are −1l,−ωl,−ωl2
∴ b3+2c3−3a2−6β3−8γ3
=0+2−3(−1)3−6(−ω)3−8(−ω2)3
=2+3+6ω3+8ω6
=5+6+8=19
Explanation
Given cubic equation is :
x3+bx+c=0
∴ α,β,γ are the roots of above equation.
And βγ=1=−a
So, product of roots =−c
⇒αβγ=−c
⇒(−1)(1)=−c
⇒c=1
Since, α=−1 is the root. So,
⇒−1−b+c=0
⇒c−b=1
⇒1−b=1⇒b=0
The given equation becomes x3+1=0
So, roots are −1l,−ωl,−ωl2
∴ b3+2c3−3a2−6β3−8γ3
=0+2−3(−1)3−6(−ω)3−8(−ω2)3
=2+3+6ω3+8ω6
=5+6+8=19