Respuesta :

nobillionaireNobley
[tex]cos2a= cos^{2} a- sin^{2} a \\ but \ cos^{2} a + sin^{2} a=1 \\ i.e. \ cos^{2} a=1- sin^{2} a[/tex]
Therefore,
[tex]cos2a=1- sin^{2} a- sin^{2} a \\ =1-2 sin^{2} a[/tex]
turanganik

true (just did this on apex)