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Complex Numbers and Quadratic Equations — Maths STD 11 Science — Question

CBSE BoardEnglish MediumSTD 11 ScienceMathsComplex Numbers and Quadratic Equations1 Mark
MCQ
Solve $2x^2+ x + 1 = 0.$
  • ✓
    $\frac{-1\pm\text{i}\sqrt{7}}{4}$
  • B
    $\frac{1\pm\text{i}\sqrt{7}}{4}$
  • C
    $\frac{1\pm\sqrt{7}}{4}$
  • D
    $\frac{​​-1\pm\sqrt{7}}{4}$
✓

Answer

Correct option: A.
$\frac{-1\pm\text{i}\sqrt{7}}{4}$
$2\text{x}^2+\text{x}+1=0$
$\text{D}=1^2-4\times2\times1=1-8=-7\leq0$
Since $\text{D}\leq0,$ imaginary roots are there.
$\Rightarrow\text{x}=\frac{-1\pm\sqrt{1^2-42.1}}{2.2}=\frac{-1\pm\text{i}\sqrt{7}}{4}$

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