Understanding the Real Part of a Complex Number

A complex number is generally expressed in the standard form a + bi, where:

• a is the real part.
• b is the imaginary part.
• i is the imaginary unit, defined as $i = \sqrt{-1}$.

Identifying the Real Part of $5i$

The given number is $5i$. This is a purely imaginary number.

To find its real part, we can write $5i$ in the standard form a + bi:

$5i = 0 + 5i$

Comparing $0 + 5i$ to the standard form a + bi:

• The value of a (the real part) is 0.
• The value of b (the imaginary part) is 5.

Therefore, the real part of the number $5i$ is 0.