1.jika alfa dan beta adalah sudut lancip dengan sin alfa = 4/5 dan beta 12/13. tentukan a.cos (alfa + beta) b.cos (alfa -beta) makasih ya..

[tex]sin \alpha = \frac{4}{5} \\ cos \beta = \frac{12}{13} \\ \\ a. \\ cos( \alpha + \beta ) \\ =cos \alpha .cos \beta-sin \alpha .sin \beta \\ = \frac{3}{5} . \frac{12}{13}- \frac{4}{5}. \frac{5}{13} \\ = \frac{36}{65} - \frac{20}{65} \\ = \frac{16}{65} \\ \\ b. \\ cos( \alpha - \beta ) \\ =cos \alpha .cos \beta +sin \alpha .sin \beta \\ = \frac{3}{5}. \frac{12}{13} + \frac{4}{5}. \frac{5}{13} \\ =\frac{36}{65} + \frac{20}{65} \\ = \frac{56}{65} [/tex]