Bukan merupakan solusi dari cos 2a + sin a = 0,0° ≤ a ≤ 450°
cos2a + sina = 0
1-2sin²a + sina = 0
-2sin²a + sina + 1 = 0
_______________×-1
2sin²a – sina – 1 = 0
misal: sina = p
2p² – p – 1 = 0
(2p+1)(p-1) = 0
2p+1 = 0 v p=1
2p = -1
p = -1/2
sin x = -1/2
x = {210°, 330}
sinx = 1
x = {90}
x= 90 + k.360
k= 1 → x = 90+360= 450
Jadi, HP = {90,210,330,450}