jawaban
y'=0
-2sin2x+1=0
sin2x=½
2x=30+k.360
x=15+k.180
x=15, 195
atau
2x=180-30+k.360
x=75+k180
x=75, 255
f(15°)=cos30+π/12=½√3+π/12
f(75°)=cos150+5π/12=-½√3+5π/12
titik maksimum=(15°, ½√3+π/12) atau (195°, ½√3+π/12)
titik minimum=(75°,-½√3+5π/12) atau (255°,-½√3+5π/12)