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Materi trigonometri
Rumus cosinus
AC = 12cm
AB = 8cm
A = 60°

[tex] {bc}^{2} = {ac}^{2} + {ab}^{2} - 2(ac)(ab)( \cos(a) ) \\ bc^{2} = {12}^{2} + {8}^{2} - 2(12)(8)( \cos(60)) \\ {bc}^{2} = 144 + 64 - 2(12)(8)( \frac{1}{2} ) \\ {bc}^{2} = 208 - 96 \\ {bc}^{2} =112 \\ bc = \sqrt{112} \\ bc = \sqrt{16 \times 7} \\ bc = \sqrt{16} \sqrt{7} \\ bc = 4 \sqrt{7} [/tex]
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