If the two angles are complementary, their measures add up to 90 degrees. Given the measures of the angles are \((2x + 3)^\circ\) and \(2x^\circ\), we can set up the equation as follows:
\[ (2x + 3) + 2x = 90 \]
Now we can simplify and write the equation in the requested format:
\[ (2x + 3)^\circ + 2x^\circ = 90^\circ \]
So, the complete equation is:
\[ (2x + 3)° + 2x° = 90° \]