Posted by Purplechick4 on Wednesday, February 8, 2012 at 12:56am.
pi < x < 3 pi / 2
180 ° < x < 270 °
That is Quadran III
In Quadran III cosine are negative.
cos ( x ) = + OR - 1 /sqrt [ 1 + tan( x ) ^ 2 ]
In this case :
cos ( x ) = - 1 / sqrt [ 1 + tan( x ) ^ 2 ]
cos ( x ) = - 1 / sqrt [ 1 + ( 9 / 4 ) ^ 2 ]
cos ( x ) = - 1 / sqrt ( 1 + 81 / 16 )
cos ( x ) = - 1 / sqrt ( 16 / 16 + 81 / 16 )
cos ( x ) = - 1 / sqrt ( 97 / 16 )
cos ( x ) = - 1 / [ sqrt ( 97 ) / 4 ]
cos ( x ) = - 4 / sqrt ( 97 )
Thanks(:
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