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<p><br>Mencari \cos \alpha:<br>\cos^2 \alpha = 1 - \sin^2 \alpha<br>\cos^2 \alpha = 1 - \left(\frac{3}{5}\right)^2<br>\cos^2 \alpha = 1 - \frac{9}{25}<br>\cos^2 \alpha = \frac{25}{25} - \frac{9}{25}<br>\cos^2 \alpha = \frac{16}{25}<br>\cos \alpha = \sqrt{\frac{16}{25}}<br>\cos \alpha = \frac{4}{5} (Diasumsikan \alpha berada di kuadran I, sehingga \cos \alpha positif)<br>Mencari \cos \beta:<br>\cos^2 \beta = 1 - \sin^2 \beta<br>\cos^2 \beta = 1 - \left(\frac{7}{25}\right)^2<br>\cos^2 \beta = 1 - \frac{49}{625}<br>\cos^2 \beta = \frac{625}{625} - \frac{49}{625}<br>\cos^2 \beta = \frac{576}{625}<br>\cos \beta = \sqrt{\frac{576}{625}}<br>\cos \beta = \frac{24}{25} (Diasumsikan \beta berada di kuadran I, sehingga \cos \beta positif)<br>Sekarang substitusikan nilai-nilai yang sudah kita dapatkan ke dalam rumus \cos(\alpha + \beta):<br>\cos(\alpha + \beta) = \left(\frac{4}{5}\right) \left(\frac{24}{25}\right) - \left(\frac{3}{5}\right) \left(\frac{7}{25}\right)<br>\cos(\alpha + \beta) = \frac{96}{125} - \frac{21}{125}<br>\cos(\alpha + \beta) = \frac{96 - 21}{125}<br>\cos(\alpha + \beta) = \frac{75}{125}<br>Sederhanakan pecahan dengan membagi pembilang dan penyebut dengan 25:<br>\cos(\alpha + \beta) = \frac{75 \div 25}{125 \div 25}<br>\cos(\alpha + \beta) = \frac{3}{5}<br>Jadi, nilai dari \cos(\alpha + \beta) adalah \frac{3}{5}.<br>&nbsp;</p>