djcandy261 djcandy261

27-06-2017
Mathematics

contestada

The sign of the value of cos 112.5º is _____?

Respuesta :

mathelp00 mathelp00

27-06-2017

Hello,
using double angle formulas:
cos 112.5º= cos (225/2)º= -√[(1+cos 225º)/2)];

1+cos 225º=1-√2/2=(2-√2)/2
(1+cos 225º)/2)=(2-√2)/4
-√[(1+cos 225º)/2)]=-√(2-√2)/2
cos 112.5º=-√(2-√2)/2
bye :-)

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