![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=66136d2f09ffafadb8f2617e8531cb88.png\")
.(5) The double angle formula for cosine function : .
The trigonometric function value of ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=1e6d35ebd33c6f1722886c14fb21f301.png\")
that means angle ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=487d638a20e522fdfc94c003e0a706de.png\")
lies in III quadrant.
Substitute the value of ![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=823fa33276ff8753b23b4c1c153ea214.png\")
in ![\"\"](\"http://www.mathskey.com/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=66136d2f09ffafadb8f2617e8531cb88.png\")
.
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=4662a5614bd9017081196d49fd055c3b.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=0c8553b33a322eeaec108dc9ad1665ff.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=c2258288e9128df12b66e7f37acb8845.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=d0d26bcff2ca995a77b8c32141651103.png\")
![\"\"](\"/test/fckeditor/editor/plugins/fckeditor_wiris/integration/showimage.php?formula=3a234bc66a536450591f13c4b3d4ca12.png\")
.
Option C is correct answer.