Exercise · ZW-COMPLEX-MODULUS-008 · ★★☆ Intermediate
For which real \(t\) does \(|t+3i|=5\) hold?
Choose one option.
Show answer
- C. \(t=4\) or \(t=-4\)
Explanation
\(t^2+9=25\) gives \(t^2=16\), so \(t=\pm4\). Forgetting the negative root is the typical mistake.
Review the concept: Modulus of a complex number
The modulus \(|z|\) of a complex number \(z=a+bi\) is the distance from the point \((a,b)\) to the origin of the complex plane.
\[|z|=\sqrt{a^2+b^2}=\sqrt{z\bar z}\]
More practice problems: modulus of a complex number
- ZW-COMPLEX-MODULUS-001 Compute |3+4i|.
- ZW-COMPLEX-MODULUS-002 What is |-5+12i|?
- ZW-COMPLEX-MODULUS-003 Compute |1-i|.
- ZW-COMPLEX-MODULUS-004 For a complex z, what does zbar z equal?
- ZW-COMPLEX-MODULUS-005 Which set does |z-(1+i)|=2 describe?
- ZW-COMPLEX-MODULUS-006 Compute |(1+i)(3-4i)|.
- ZW-COMPLEX-MODULUS-007 Compute |(6+8i)/(3-4i)|.
- ZW-COMPLEX-MODULUS-009 If |z|=3 and |w|=4, what is the smallest possible value of |z+w|?