tlong bantu, aq blm faham

ambil titik tengah antara A dan C, beri nama titik I
[tex]ib = 2 \sqrt{2} \: cm \\ fb = 4 \: cm[/tex]
[tex]if = \sqrt{ {(2 \sqrt{2} )}^{2} + {4}^{2} } \\ \: \: \: \: \: = \sqrt{8 + 16} \\ \: \: \: \: \: = \sqrt{24} = 2 \sqrt{6} [/tex]

[tex] \cos \alpha = \frac{4}{2 \sqrt{6} } = \frac{2}{ \sqrt{6} } \times \frac{ \sqrt{6} }{ \sqrt{6} } \\ \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: = \frac{2 \sqrt{6} }{6} = \frac{1}{3} \sqrt{6} [/tex]