Réitigh cos(3pidiv8)

$$\cos ( 3 \pi \div 8 )$$

Luacháil

$$\frac{\sqrt{2-\sqrt{2}}}{2}\approx 0.382683432$$

Céimeanna Réitigh

Bain úsáid as \cos(x+y)=\cos(x)\cos(y)-\sin(y)\sin(x) nuair atá x=\frac{\pi }{2} agus y=\frac{\pi }{4}ann chun an toradh a fháil.

$$\cos(\frac{\pi }{2}+\frac{\pi }{4})=\cos(\frac{\pi }{2})\cos(\frac{\pi }{4})-\sin(\frac{\pi }{4})\sin(\frac{\pi }{2})$$

Faigh luach do\cos(\frac{\pi }{2})ón dtábla luachanna triantánúla.

$$0\cos(\frac{\pi }{4})-\sin(\frac{\pi }{4})\sin(\frac{\pi }{2})$$

Faigh luach do\cos(\frac{\pi }{4})ón dtábla luachanna triantánúla.

$$0\times \frac{\sqrt{2}}{2}-\sin(\frac{\pi }{4})\sin(\frac{\pi }{2})$$

Faigh luach do\sin(\frac{\pi }{4})ón dtábla luachanna triantánúla.

$$0\times \frac{\sqrt{2}}{2}-\frac{\sqrt{2}}{2}\sin(\frac{\pi }{2})$$

Faigh luach do\sin(\frac{\pi }{2})ón dtábla luachanna triantánúla.

$$0\times \frac{\sqrt{2}}{2}-\frac{\sqrt{2}}{2}\times 1$$

Déan áirimh.

$$-\frac{\sqrt{2}}{2}$$