JEE Mains · Maths · STD 11 - 4.2 Quadratic equations and inequations
Let \(\alpha \) and \(\beta \) be two roots of the equation \(x^2 + 2x + 2 = 0\) , then is equal to \({\alpha ^{15}} + {\beta ^{15}}\) is equal to
- A \(-256\)
- B \(512\)
- C \(-512\)
- D \(256\)
Answer & Solution
Correct Answer
(A) \(-256\)
Step-by-step Solution
Detailed explanation
\(x^{2}+2 x+2=0\) \(\Rightarrow(x+1)^{2}=-1\) \(x=-1 \pm i=\sqrt{2} e^{i\left(\pm \frac{3 \pi}{4}\right)}\) \(\therefore \alpha^{15}, \beta^{15}=(\sqrt{2})^{15} \times 2 \cos \left(15 . \frac{3 \pi}{4}\right)\) \(=2^{8} \sqrt{2} \times\left(-\frac{1}{\sqrt{2}}\right)=-256\)
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