Magnitude of a Complex Number

Consider the complex number $z = 3 + 4i$. If $z$ is expressed in polar form as $z = r( ext{cos} heta + i ext{sin} heta)$, where $r$ is the magnitude of $z$ and $ heta$ is the argument of $z$, what is the value of $r$?

To find $r$, use the formula: $$r = ext{sqrt}(a^2 + b^2)$$ where $a$ is the real part and $b$ is the imaginary part of the complex number.