I)
Vis at:
[tex]\tan(\frac{x}{2})=\cot(\frac{x}{2})\,-\,2\cot(x)[/tex]
II)
Vis at den n'te deriverte til [tex]\,\,\sin^4(x)+\cos^4(x)=4^{n-1}\,\cos(4x+n\frac{\pi}{2})[/tex]
dvs
[tex]\frac{d^n}{dx^n}\,\left(\sin^4(x)+\cos^4(x)\right)=4^{n-1}\,\cos(4x+n\frac{\pi}{2})[/tex]
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