2cos15(sin15+cos15)-1

jawab

2 cos 15 ( sin 15  + cos 15) - 1 =
= 2 cos 15 sin  15 + 2 cos² 15 - 1
= (2 sin 15 cos 15) + (2 cos² 15 -1)
= (sin 2(15)) + (cos 2(15))
= sin  30 + cos 30
= 1/2 + 1/2√3
= 1/2 (1 + √3)