Chapter 6 - Section 6.5 - Complex Numbers in Polar Form; DeMoivre's Theorem - Exercise Set - Page 767: 6

$$\sqrt{29}$$

We plot the complex number $z=2+5i$ the same way we plot $(2,5)$ in the rectangular coordinate system. We find the absolute value of the complex number as follows.$$|z|=|a+bi|=\sqrt{a^2+b^2} \\ \Rightarrow \quad |z|=|2+5i|=\sqrt{2^2+5^2}=\sqrt{29}$$