271.

Adicione formule

TEKST ZADATKA

Uprostiti izraz:

cos(x+y)cos(xy)\cos{(x+y)}\cos{(x-y)}

REŠENJE ZADATKA

Primeniti formulu za kosinus zbira dva ugla: cos(α+β)=cosαcosβsinαsinβ \cos{(\alpha+\beta)}=\cos{\alpha}\cos{\beta}-\sin{\alpha}\sin{\beta}

(cosxcosysinxsiny)cos(xy)(\cos{x}\cos{y}-\sin{x}\sin{y})\cos{(x-y)}

Primeniti formulu za kosinus razlike dva ugla: cos(αβ)=cosαcosβ+sinαsinβ \cos{(\alpha-\beta)}=\cos{\alpha}\cos{\beta}+\sin{\alpha}\sin{\beta}

(cosxcosysinxsiny)(cosxcosy+sinxsiny)(\cos{x}\cos{y}-\sin{x}\sin{y})(\cos{x}\cos{y}+\sin{x}\sin{y})

Osloboditi se zagrada:

cosxcosycosxcosy+cosxcosysinxsinysinxsinycosxcosysinxsinysinxsiny\cos{x}\cos{y} \cdot \cos{x}\cos{y}+\cos{x}\cos{y}\cdot \sin{x}\sin{y}-\sin{x}\sin{y}\cdot \cos{x}\cos{y}-\sin{x}\sin{y}\cdot\sin{x}\sin{y}

Srediti izraz.

cos2xcos2ysin2xsin2y\cos^2{x}\cos^2{y} -\sin^2{x}\sin^2{y}

Primeniti osnovnu relaciju između trigonometrijskih funkcija: sin2α+cos2α=1\sin^2{\alpha}+\cos^2{\alpha}=1 , gde je cos2x=1sin2x\cos^2x=1-\sin^2x i sin2y=1cos2y \sin^2y=1-\cos^2y

(1sin2x)cos2ysin2x(1cos2y)(1-\sin^2{x})\cos^2{y} -\sin^2{x}(1-\cos^2y)

Osloboditi se zagrada:

cos2ysin2xcos2ysin2x+sin2xcos2y=cos2ysin2x\cos^2{y}-\sin^2{x}\cos^2{y} -\sin^2{x} + \sin^2x\cos^2y=\cos^2{y}-\sin^2x

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