(1 + sin x) ( 1 - sin x) = cos²x

[tex](1 + \sin \: x)(1 - \sin \: x) = \cos^{2} x \\ 1 - \sin^{2}x = \cos^{2} x \\ 1 = \cos^{2} x + \sin^{2}x \\ 1 = 1[/tex]
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