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If alpha,beta gamma are zeroes of cubic ...

If `alpha,beta gamma` are zeroes of cubic polynomial `x^(3)+5x-2`, then find the value of `alpha^(3)+beta^(3)+gamma^(3)`.

A

`2`

B

`3`

C

`6`

D

None

Text Solution

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The correct Answer is:
To find the value of \( \alpha^3 + \beta^3 + \gamma^3 \) where \( \alpha, \beta, \gamma \) are the roots of the polynomial \( x^3 + 5x - 2 \), we can follow these steps: ### Step 1: Identify the coefficients of the polynomial The given polynomial is \( x^3 + 5x - 2 \). We can compare this with the general form of a cubic polynomial \( ax^3 + bx^2 + cx + d \): - \( a = 1 \) - \( b = 0 \) (since there is no \( x^2 \) term) - \( c = 5 \) - \( d = -2 \) ### Step 2: Calculate the sum of the roots The sum of the roots \( \alpha + \beta + \gamma \) for a cubic polynomial is given by the formula: \[ \alpha + \beta + \gamma = -\frac{b}{a} \] Substituting the values: \[ \alpha + \beta + \gamma = -\frac{0}{1} = 0 \] ### Step 3: Calculate the sum of the product of the roots taken two at a time The sum of the product of the roots taken two at a time \( \alpha\beta + \beta\gamma + \gamma\alpha \) is given by: \[ \alpha\beta + \beta\gamma + \gamma\alpha = \frac{c}{a} \] Substituting the values: \[ \alpha\beta + \beta\gamma + \gamma\alpha = \frac{5}{1} = 5 \] ### Step 4: Calculate the product of the roots The product of the roots \( \alpha\beta\gamma \) is given by: \[ \alpha\beta\gamma = -\frac{d}{a} \] Substituting the values: \[ \alpha\beta\gamma = -\frac{-2}{1} = 2 \] ### Step 5: Use the formula for the sum of cubes The formula for the sum of cubes of the roots is: \[ \alpha^3 + \beta^3 + \gamma^3 = (\alpha + \beta + \gamma)^3 - 3(\alpha + \beta)(\beta + \gamma)(\gamma + \alpha) \] Since we already found \( \alpha + \beta + \gamma = 0 \), we can simplify: \[ \alpha^3 + \beta^3 + \gamma^3 = 0^3 - 3(\alpha\beta + \beta\gamma + \gamma\alpha)(\alpha + \beta + \gamma) \] Substituting the known values: \[ \alpha^3 + \beta^3 + \gamma^3 = 0 - 3(5)(0) = 0 \] ### Step 6: Calculate the final value Thus, we have: \[ \alpha^3 + \beta^3 + \gamma^3 = 0 + 3 \cdot 2 = 6 \] ### Final Answer The value of \( \alpha^3 + \beta^3 + \gamma^3 \) is \( 6 \). ---

To find the value of \( \alpha^3 + \beta^3 + \gamma^3 \) where \( \alpha, \beta, \gamma \) are the roots of the polynomial \( x^3 + 5x - 2 \), we can follow these steps: ### Step 1: Identify the coefficients of the polynomial The given polynomial is \( x^3 + 5x - 2 \). We can compare this with the general form of a cubic polynomial \( ax^3 + bx^2 + cx + d \): - \( a = 1 \) - \( b = 0 \) (since there is no \( x^2 \) term) - \( c = 5 \) - \( d = -2 \) ...
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