Complex Numbers
Modulus inequalities and distance from origin
GRB_1000_MCQ
Grade Class 12
Question:
If the complex number $z$ satisfies the condition $\left|z - \dfrac{25}{z}\right| = 24$, then which of the following is(are) <b>correct</b>?
Maximum distance of $z$ from origin is 5
Maximum distance of $z$ from origin is 25
Minimum distance of $z$ from origin is 1
Minimum distance of $z$ from origin is 4
Step-by-Step Solution
Step 1: Let $r = |z|$. Apply the triangle inequality to $\left|z - \dfrac{25}{z}\right| = 24$:
$$\left||z| - \left|\frac{25}{z}\right|\right| \leq \left|z - \frac{25}{z}\right| \leq |z| + \left|\frac{25}{z}\right|$$
$$\left|r - \frac{25}{r}\right| \leq 24 \leq r + \frac{25}{r}$$
Step 2: From $\left|r - \dfrac{25}{r}\right| \leq 24$, we get $-24 \leq r - \dfrac{25}{r} \leq 24$.
Step 3: From $r - \dfrac{25}{r} \leq 24$: $r^2 - 24r - 25 \leq 0 \Rightarrow (r-25)(r+1) \leq 0 \Rightarrow r \leq 25$ (since $r > 0$).
Step 4: From $r - \dfrac{25}{r} \geq -24$: $r^2 + 24r - 25 \geq 0 \Rightarrow (r+25)(r-1) \geq 0 \Rightarrow r \geq 1$ (since $r > 0$).
Step 5: Therefore $1 \leq r \leq 25$, meaning the minimum distance from origin is $1$ and maximum distance is $25$.
Step 6: The correct options are **(b) Maximum distance is 25** and **(c) Minimum distance is 1**.
Correct Answer: 2, 3