gaokao 2015 Q9

gaokao · China · tianjin-science 5 marks Complex Numbers Arithmetic Systems of Equations via Real and Imaginary Part Matching

i is the imaginary unit. If the complex number $(1 - 2i)(a + i)$ is a pure imaginary number, then the real number a equals .

i is the imaginary unit. If the complex number $(1 - 2i)(a + i)$ is a pure imaginary number, then the real number a equals \underline{\hspace{2cm}}.