En el intervalo 0º = ≤x ≤180º determina la solucion desen²x - cos²x - 1 / 2 = 0?

Tienes lo siguiente :

Debes recordar esta identidad :

<img src="https://tex.z-dn.net/?f=sen%5E2x%2Bcos%5E2x%3D1%20%5C%5C%20%5Cto%20sen%5E2x%3D1-cos%5E2x" />

Dejas todo en términos de seno o coseno :

<img src="https://tex.z-dn.net/?f=sen%5E2x-cos%5E2x-1%2F2%3D0%20%5C%5C%20%3D1-cos%5E2x-cos%5E2x-1%2F2%5C%5C%3D1%2F2-2cos%5E2x%3D0%5C%5C2%281%2F2-2cos%5E2x%29%3D0%5C%5C%3D1-4cos%5E2x%3D%281%2B2cosx%29%281-2cosx%29%5C%5C%20%5C%5C1%2B2cosx%3D0%5Cto%20cosx%3D-1%2F2%5Cto%20x%3Darccos%28-1%2F2%29%3D120%5C%C2%B0%5C%5C1-2cosx%3D0%5Cto%20cosx%3D1%2F2%5Cto%20x%3Darccos%281%2F2%29%3D60%5C%C2%B0" />

Saludos!