Now combine with \( \cos^2(\phi) = \frac12 \). The only solution satisfying both is \( \phi = -\frac\pi4 \) (since \( \phi = \frac\pi4 \) would give \( \cos^2 = \frac12 \), but \( \cos\left(\frac\pi2 + \frac\pi4\right) = \cos\left(\frac3\pi4\right) = -\frac1\sqrt2 \), not zero). However, satisfying \( \cos\left(\frac\pi2 + \phi\right) = 0 \) implies: - Portal da Acústica