Jawabanmu

2013-12-08T11:10:40+07:00
4 * cos 75
= 4 * ( cos(45+30) )
= 4 * (cos 45 * cos 30 - sin 45 * sin 30)
= 4 * (√2/2 . √3/2 - √2/2 . 1/2)
= 4 * (√6/4 - √2/4)
=  4 * ((√6 - √2) / 4 )
√6 - √2
2013-12-08T11:55:34+07:00
cos 75 =  \frac{ \sqrt{6} -\sqrt{2}  }{4}

4 . cos 75 = 4.  \frac{ \sqrt{6} -\sqrt{2}  }{4}
                =  \sqrt{6}- \sqrt{2}

dalam kalimat:
4 dikali cos 75 = 4 dikali akar(6) - akar(2) per (4)
                      = akar(6) - akar(2)
selesai.