Complex Numbers
Modulus Equations
Complex Numbers_PYQ
Grade 11

Question:

Let $z$ be a complex number such that $|z|+z=3+i$ (where $i=\sqrt{-1}$). Then $|z|$ is equal to
$\dfrac{\sqrt{34}}{3}$
$\dfrac{5}{3}$
$\dfrac{\sqrt{41}}{4}$
$\dfrac{5}{4}$

Step-by-Step Solution

Key Concept: Since $|z|$ is real, equating imaginary parts directly gives $\text{Im}(z)$, reducing the problem to one real equation in $\text{Re}(z)$.
**Step 1: Separate real and imaginary parts** Let $z=x+iy$. Then $|z|+x+iy=3+i$. Imaginary part: $y=1$. Real part: $|z|+x=3$. **Step 2: Solve for x** $\sqrt{x^2+1}=3-x$. Squaring (valid since $x<3$): $x^2+1=9-6x+x^2 \Rightarrow 6x=8 \Rightarrow x=\dfrac{4}{3}$. **Step 3: Compute |z|** $|z|=\sqrt{\left(\dfrac{4}{3}\right)^2+1^2}=\sqrt{\dfrac{16+9}{9}}=\dfrac{5}{3}$.
Correct Answer: 2

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