why cos of -theta = cos theta?????... can any body explain it??

cos(-x)=cos(x)..........because of cos is an even function i.e., f(-x)=f(x) here negative becomes positive ….….….…..all over Trigonometric ratios:

sin(-x)=-sinx

tan(-x)=-tanx

cot(-x)=-cotx

cosec(-x)=-cosecx......................these 4 are odd functions but where as..

 

cos(-x)=cosx

sec(-x)=secx.................these 2 are even functions......

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(cos(-x)=cos(x)..........because of cos is an even function i.e., f(-x)=f(x) here negative becomes positive ….….….…..all over Trigonometric ratios,) :- how they became positive ???