Respuesta :

altavistard

Answer:

Step-by-step explanation:

The cosine of angle Ф is √(1 - sin²Ф), which is positive if our angle 81 degrees is in Quadrant I.

sin 81° = 0.9877, so (sin 81°)² = 0.9755, and

cos 81° = 1 - 0.9755 = 0.0245