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Aratati ca 1/(sin60°- sin30°)(cos60°+cos30°) apartine lui N

Răspuns :

1/[(sin60°-sin30°)(cos60°+cos30°)]=[tex] \frac{1}{( \frac{ \sqrt{3} }{2}- \frac{1}{2})( \frac{1}{2}+ \frac{ \sqrt{3} }{2}) }= [/tex][tex] \frac{1}{ \frac{3}{4}- \frac{1}{4} } = \frac{1}{ \frac{2}{4} }=2 [/tex] ∈ N