How to Solve Rationalizing Imaginary Denominators? (+FREE Worksheet!)

Related Topics

• How to Multiply and Divide Complex Numbers
• How to Add and Subtract Complex Numbers

Step by step guide to rationalizing Imaginary Denominators

• Step 1: Find the conjugate (it’s the denominator with different sign between the two terms.
• Step 2: Multiply the numerator and denominator by the conjugate.
• Step 3: Simplify if needed.

Rationalizing Imaginary Denominators – Example 1:

Solve: $\frac{2-3i}{6i}$

Solution:

Multiply by the conjugate: $\frac{-i}{-i}$:
$\frac{2-3i}{6i}=\frac{(2-3i)(-i)}{6i(-i) }=\frac{-3-2i}{6}=-\frac{1}{2}-\frac{1}{3} i$

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Rationalizing Imaginary Denominators – Example 2:

Solve: $\frac{8i}{2 – 4i}$

Solution:

Factor $2 – 4i=2(1-2i)$, then: $\frac{8i}{2(1-2i)}=\frac{4i}{(1-2i)}$
Multiply by the conjugate $\frac{1+2i}{1+2i}$:

$\frac{4i}{1- 2i}= \frac{4i(1+2i)}{(1-2i)(1+2i)}=\frac{-8+4i}{5}=-\frac{8}{5}+\frac{4}{5} i$

Rationalizing Imaginary Denominators – Example 3:

Solve: $\frac{5i}{2 – 3i}$

Solution:

Multiply by the conjugate: $\frac{2+ 3i}{2+ 3i}$:

$\frac{5i}{2 – 3i}=\frac{5i(2+ 3i)}{(2-3i)(2+ 3i)}=\frac{-15+10i}{(2-3i)(2+ 3i)}$
Use complex arithmetic rule: $(a+bi)(a-bi)=a^2+b^2$
$(2-3i)(2+ 3i)=-2^2+(-3)^2=4+9=13$ ,

Then: $\frac{-15+10i}{(2-3i)(2+ 3i)}=\frac{-15+10i}{13}= \frac {-15}{13}+ \frac{10}{13} i$

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Rationalizing Imaginary Denominators – Example 4:

Solve: $\frac{4-9i}{-6i}$

Solution:

Apply fraction rule: $\frac{4-9i}{-6i}=-\frac{4-9i}{6i}$
Multiply by the conjugate: $\frac{-i}{-i}$.
$-\frac{4-9i}{6i}=-\frac{(4-9i)(-i)}{6i(-i)} =-\frac{-9-4i}{6}$$=\frac {3}{2} + \frac{2}{3}i$

Exercises for Solving Rationalizing Imaginary Denominators

Simplify.

• $\color{blue}{\frac{10 – 10i}{- 5i}} \\\ $
• $\color{blue}{\frac{5 – 8i}{- 10i}} \\\ $
• $\color{blue}{\frac{6 + 8i}{9i}} \\\ $
• $\color{blue}{\frac{8i}{-1+3i}} \\\ $
• $\color{blue}{\frac{5i}{- 2 – 6i}} \\\ $
• $\color{blue}{\frac{- 10 – 5i}{- 6 + 6i}} \\\ $

Download Rationalizing Imaginary Denominators Worksheet

• $\color{blue}{2+ 2i} \\\ $
• $\color{blue}{\frac{4}{5}+\frac {1}{2}i} \\\ $
• $\color{blue}{\frac{8}{9}-\frac{2}{3}i} \\\ $
• $\color{blue}{\frac{12}{5}-\frac{4}{5}i}\\\ $
• $\color{blue}{\frac{-3}{4}-\frac{1}{4}i} \\\ $
• $\color{blue}{\frac{5}{12}+\frac{5}{4}i} \\\ $

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