tentukan nilai dari cos 5/4 phi

phi = 180°
5/4 x 180°
= 5(45)
= 225°
cos 225° = -1/2√2

maaf kalo salah

phi = 180°
5/4 phi = 5/4 x 180 = 225°

cos 225° = cos(270-45)°

cos(270-45)° = - sin45°
                      = -1/2 √2