Antwort
$\sin(x) = \cos(90^\circ - x)$ or in radians $\sin(x) = \cos\left(\frac{\pi}{2} - x\right)$.
Erklärung
Since acute angles in a right triangle sum to $90^\circ$, the side opposite angle $x$ is adjacent to $(90^\circ - x)$, making the ratios identical.