[tex]sin^{4}\alpha-cos^{4}\alpha + cos^{2}\alpha =\\\\=(sin^{2}\alpha+cos^{2}\alpha)(sin^{2}\alpha-cos^{2}\alpha) + cos^{2}\alpha=\\\\=1\cdot(sin^{2}\alpha - cos^{2}\alpha) + cos^{2}\alpha =\\\\=sin^{2}\alpha - cos^{2}\alpha + cos^{2}\alpha = \boxed{sin^{2}\alpha}\\\\\underline{Odp. \ C. \ sin^{2}\alpha}[/tex]
