JEE Advanced · Mathematics · 3. Complex Numbers
Let \(z\) be a complex number such that the imaginary part of \(z\) is non-zero and \(a=z^{2}+z+1\) is real. Then a cannot take the value
- A \(-1\)
- B \(\frac{1}{3}\)
- C \(\frac{1}{2}\)
- D \(\frac{3}{4}\)
Answer & Solution
Correct Answer
(D) \(\frac{3}{4}\)
Step-by-step Solution
Detailed explanation
\(\because \operatorname{Im}(z) \neq 0\) \(\Rightarrow \quad z\) is non-real and equation \(z^{2}+z+(1-a)=0\) will have non-real roots, if \(D < 0\)
\(\Rightarrow 1-4(1-a) < 0\) \(\Rightarrow \quad 4 a < 3 \Rightarrow a < \frac{3}{4}\)
\(\therefore a\) can not take the value \(\frac{3}{4}\).
\(\Rightarrow 1-4(1-a) < 0\) \(\Rightarrow \quad 4 a < 3 \Rightarrow a < \frac{3}{4}\)
\(\therefore a\) can not take the value \(\frac{3}{4}\).
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