Jawabanmu

2014-07-24T00:37:51+07:00
Menggunakan rumus cos
(bc)² = (ac)² + (ab)² -2(ac).(ab).cos a
64 = 49 + 36 -2.7.6.cos a
64 = 85 - 84.cos a
84.cos a =85-64
84.cos a = 21
cos a = 21/84
cos a = 1/4
1 5 1
2014-07-24T01:08:41+07:00
(BC)² = (AB)² + (AC)² - 2(AB)(AC)cos A
64 = 36 + 49 - (2)(6)(7) cos A
64 = 85 - (84) cos A
(84) cos A = 85 - 64
(84) cos A = 21
cos A = 21/84
cos A = 1/4