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Simplify the following, tan -x cos -x

User Jone
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1 Answer

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Tan(A)=sin(A) / cos(A)
so
tan(A)*cos(A)=sin(A)/cos(A)*cos(A)
=sin(A) [ by cancelling cos(A) ]

substitute -x for A, then
tan(-x)cos(-x) = sin(-x)
[ provided cos(-x) does not equal zero, i.e. x does not equal (k+1/2)pi where k is an integer ]
User Geeky I
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