Complementary angles are two angles whose measures add up to 90 degrees. Given the measures of the two angles are \((x + 3)^\circ\) and \((4x - 2)^\circ\), we can set up the equation as follows:
\[ (x + 3) + (4x - 2) = 90 \]
So, the complete equation representing the measures of the angles is:
\[ (x + 3)^\circ + (4x - 2)^\circ = 90^\circ \]