sin 30=1/2 ; 2cos 60=2* 1/2 ; 6tg 30=6* √3/3 ; ctg 30 =√3/3.
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cos 30=√3/2 ; 6*cos 30=6*√3/2 ; cos 30=√3/2
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cos 30-2* cos 60-6* cos 30: cos 30<=>√3/2-2*1/1-6*√3/2:√3/2=>√3/2-2-6√3/2*2/√3=>√3/2-2-6=>√3/2-4=>8√3/2=>4√3