[tex]\sqrt[2]{15} / 4[/tex]
Aplicando-se a equação fundamental da trigonometria tem-se:
[tex]sen^2x + cos^2x = 1\\\\(1/4)^2 + cos^2x = 1\\\\1/16 + cos^2x= 1\\\\cos^2x = 1 - 1/16\\\\cos^2x = (16 - 1) / 16\\\\cos^2x = 15 / 16\\\\cosx = \sqrt[2]{\frac{15}{16} }\\\\cox = \sqrt[2]{15} / 4\\\\[/tex]
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