To solve the equation \( \sin(x + 12°) = \cos(18° + 2x) \), we utilize the identity \( \cos(θ) = \sin(90° - θ) \). Rewriting the equation gives us:
\[ \sin(x + 12°) = \sin(90° - (18° + 2x)) \]
This simplifies to:
\[ \sin(x + 12°) = \sin(72° - 2x) \]
Setting the arguments equal to each other leads to two equations. The first gives us:
\[ x + 12° = 72° - 2x \]
Solving this, we find:
\[ 3x = 60° \] \[ x = 20° \]
The second sine equation could lead to a different solution, but in this case, the values produced would not yield a valid angle when considering the constraints of a right triangle and the given equation.
For the measure of the smaller angle in the triangle, we have \( x = 20° \) and the other acute angle would be \( 90° - 20° = 70° \). Thus, the measure of the smaller angle is \( 20° \).
In summary, I set the equations from the given trigonometric identity, solved for \( x \), and determined the smaller angle from the right triangle's properties. The answers are \( x = 20° \) and the smaller angle is \( 20° \).