Trigonometria - jaumesc
Trigonometria - jaumesc
Trigonometria - jaumesc
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H. Itkur<br />
D'una suma o diferència de cosinus<br />
cos α + cos<br />
β =<br />
α+<br />
β α−<br />
β<br />
2·cos ·cos<br />
2 2<br />
Considerem a =<br />
α + β<br />
i b =<br />
2<br />
α − β<br />
⇒ α=a+b i β=a-b<br />
2<br />
llavors cos α = cos(a+b) = cos a ·cos b - sin a ·sin b (1)<br />
cos β = sin (a-b) = cos a ·cos b + sin a ·sin b (2)<br />
<strong>Trigonometria</strong> -26/<br />
32<br />
α+<br />
β α−<br />
β<br />
cos α − cos<br />
β = − 2·sin ·sin<br />
2 2<br />
Sumant (1) + (2) Restant (1) - (2)<br />
cos α +cos β= 2· cos a ·cos = =<br />
α + β α − β<br />
2·cos ·cos<br />
2 2<br />
cos α -cos β= -2· sin a ·sin b = =<br />
α +<br />
β α − β<br />
- 2·sin ·sin<br />
2 2