Odpowiedź:
Szczegółowe wyjaśnienie:
[tex]\frac{\sin^2 (90-\alpha) -\cos\alpha}{(1-\cos\alpha)^2 - \sin^2\alpha} = \frac{\cos^2 \alpha -\cos\alpha}{(1-2\cos\alpha + \cos^2\alpha) - \sin^2\alpha} = \\\frac{\cos^2 \alpha -\cos\alpha}{1- \sin^2\alpha - 2\cos\alpha + \cos^2\alpha} = \frac{\cos^2 \alpha -\cos\alpha}{ [1- \sin^2\alpha] - 2\cos\alpha + \cos^2\alpha} = \\ \frac{\cos^2 \alpha -\cos\alpha}{ [\cos^2\alpha] - 2\cos\alpha + \cos^2\alpha} = \frac{\cos^2 \alpha -\cos\alpha}{ 2\cos^2\alpha - 2\cos\alpha } = \\[/tex]
[tex]= \frac{\cos^2 \alpha -\cos\alpha}{ 2(\cos^2\alpha - \cos\alpha) } = \frac{1}{2} .[/tex]
