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If α and β  are the roots of the equation x2 - 12x + 8 = 0, what is the value of α3 + β3?
1. 234
2. 720
3. 1420
4. 1440

1 Answer

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Correct Answer - Option 4 : 1440

Concept:

If α and β are the roots of equation , ax2 + bx + c =0 

Sum of roots (α + β) = \(\rm \frac{-b}{a}\)  

Product of roots  (αβ) = \(\rm \frac{c}{a}\) 

(x + y)3 = x3 + y3 + 3xy (x + y) 

​Calculation:

x2 - 12x + 8 = 0 

α & β are the roots of the equation . 

⇒ α + β = 12  and αβ  = 8  

Now,(α + β)3 = α3 + β3 + 3αβ ( α + β ) 

⇒ (12)3 =  α3 + β3 + 3× 8 × (12)  

⇒ α3 + β3 = 1440 .

The correct option is 4. 

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