KCET · Maths · Complex Number
The modulus of the complex number
\(\frac{(1+i)^2(1+3 i)}{(2-6 i)(2-2 i)}\) is
- A \(\frac{2}{\sqrt{2}}\)
- B \(\frac{1}{\sqrt{2}}\)
- C \(\frac{\sqrt{2}}{4}\)
- D \(\frac{4}{\sqrt{2}}\)
Answer & Solution
Correct Answer
(C) \(\frac{\sqrt{2}}{4}\)
Step-by-step Solution
Detailed explanation
Here,
\(\frac{(1+i)^2(1+3 i)}{(2-6 i)(2-2 i)}\)
\(\begin{aligned} & =\frac{\left(1+i^2+2 i\right)(1+3 i)}{4-4 i-12 i+12 i^2} \\ & =\frac{2 i+6 i^2}{-8-16 i}=\frac{2 i-6}{-8-16 i} \\ & =\frac{i-3}{-4-8 i} \\ & =\frac{3-i}{(4+8 i)} \times \frac{(4-8 i)}{(4-8 i)} \\ & =\frac{12-28 i-8}{16+64} \\ & =\frac{4-28 i}{80}=\frac{1-7 i}{20} \\ & =\frac{1}{20}-\frac{7 i}{20}\end{aligned}\)
Let \(z=x+i y\)
\(\because|z|=\sqrt{x^2+y^2}\)
\(\begin{aligned} & \Rightarrow|z|=\sqrt{\left(\frac{1}{20}\right)^2+\left(\frac{7}{20}\right)^2} \\ & \Rightarrow|z|=\frac{1}{20} \sqrt{50}=\frac{5}{20} \sqrt{2} \\ & \Rightarrow|z|=\frac{\sqrt{2}}{4}\end{aligned}\)
\(\frac{(1+i)^2(1+3 i)}{(2-6 i)(2-2 i)}\)
\(\begin{aligned} & =\frac{\left(1+i^2+2 i\right)(1+3 i)}{4-4 i-12 i+12 i^2} \\ & =\frac{2 i+6 i^2}{-8-16 i}=\frac{2 i-6}{-8-16 i} \\ & =\frac{i-3}{-4-8 i} \\ & =\frac{3-i}{(4+8 i)} \times \frac{(4-8 i)}{(4-8 i)} \\ & =\frac{12-28 i-8}{16+64} \\ & =\frac{4-28 i}{80}=\frac{1-7 i}{20} \\ & =\frac{1}{20}-\frac{7 i}{20}\end{aligned}\)
Let \(z=x+i y\)
\(\because|z|=\sqrt{x^2+y^2}\)
\(\begin{aligned} & \Rightarrow|z|=\sqrt{\left(\frac{1}{20}\right)^2+\left(\frac{7}{20}\right)^2} \\ & \Rightarrow|z|=\frac{1}{20} \sqrt{50}=\frac{5}{20} \sqrt{2} \\ & \Rightarrow|z|=\frac{\sqrt{2}}{4}\end{aligned}\)
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