Since the angles are complementary, their measures add up to \(90^\circ\). Given the angles are \((2x + 3)^\circ\) and \(2x^\circ\), we can set up the equation as follows:
\[ (2x + 3) + 2x = 90 \]
Therefore, the equation for the angle measures is:
\[ (2x + 3)° + 2x° = 90° \]