kak tolong bantu dong no 46

Untuk mendapat nilai dari sin 18° bisa dilihat dari video berikut :

https://youtu.be/_00oskWLtII

sin 18° = [tex] \frac{\sqrt{5}-1}{4} [/tex]

cos 18° = [tex] \sqrt{1 - sin^218} \\ = \sqrt{1 - (\frac{\sqrt{5}-1}{4})^2} \\ = \sqrt{\frac{16-(5+1-2\sqrt{5})}{16}} \\ = \sqrt{\frac{10+2\sqrt{5}}{16}} \\ = \frac{1}{4}\sqrt{10+2\sqrt{5}} [/tex]

sin 36° = 2.sin18°.cos18°
= [tex] 2.\frac{\sqrt{5}-1}{4}.\frac{1}{4}\sqrt{10+2\sqrt{5}} \\ = \frac{(\sqrt{5}-1)(\sqrt{10+2\sqrt{5}})}{8} [/tex]