Lösung 4.3:4d
Aus Online Mathematik Brückenkurs 1
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| - | {{ | + | With the formula for double angles and the Pythagorean identity | 
| - | < | + | <math>\cos ^{2}v+\sin ^{2}v=1</math>, we can express  | 
| - | {{ | + | <math>\text{cos 2}v\text{ }</math> | 
| + | in terms of  | ||
| + | <math>\text{cos }v</math>, | ||
| + | |||
| + | |||
| + | <math>\begin{align} | ||
| + | & \text{cos 2}v=\cos ^{2}v-\sin ^{2}v=\cos ^{2}v-\left( 1-\cos ^{2}v \right) \\  | ||
| + | & =2\cos ^{2}v-1=2b^{2}-1 \\  | ||
| + | \end{align}</math> | ||
Version vom 11:48, 29. Sep. 2008
With the formula for double angles and the Pythagorean identity \displaystyle \cos ^{2}v+\sin ^{2}v=1, we can express \displaystyle \text{cos 2}v\text{ } in terms of \displaystyle \text{cos }v,
\displaystyle \begin{align}
& \text{cos 2}v=\cos ^{2}v-\sin ^{2}v=\cos ^{2}v-\left( 1-\cos ^{2}v \right) \\ 
& =2\cos ^{2}v-1=2b^{2}-1 \\ 
\end{align}
 
		  