Question:

If $\frac {2z_1} {3z_2} $ is a purely imaginary number, then $|\frac {z_1-z_2} {z_1+z_2}|$ is equal to

Updated On: Jul 6, 2022
  • $\frac {3} {2}$
  • 1
  • $\frac {2} {3}$
  • $\frac {4} {9}$
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The Correct Option is B

Solution and Explanation

Let $\frac{2z_{1}}{3z_{2}}=id$ $\therefore \left|\frac{z_{1}-z_{2}}{z_{1}+z_{2}}\right|=\left|\frac{\frac{z_{1}}{z_{2}}-1}{\frac{z_{1}}{z_{2}}-1}\right|$ $=\left|\frac{\frac{3ki}{2}-1}{\frac{3ki}{2}+1}\right|$ $=\left|\frac{3ki-2}{3ki+2}\right|=1$
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Concepts Used:

Complex Numbers and Quadratic Equations

Complex Number: Any number that is formed as a+ib is called a complex number. For example: 9+3i,7+8i are complex numbers. Here i = -1. With this we can say that i² = 1. So, for every equation which does not have a real solution we can use i = -1.

Quadratic equation: A polynomial that has two roots or is of the degree 2 is called a quadratic equation. The general form of a quadratic equation is y=ax²+bx+c. Here a≠0, b and c are the real numbers.