Oblicz bez użycia tablic i kalkulatora sin35°·cos55°+cos35°·sin55°-4cos60°
sin35°·cos55°+cos35°·sin55°-4cos60°
wzór
cos\alpha=sin(90^0-\alpha)
cos55^0=sin35^0
cos35^0=sin55^0
sin35^0 * sin35^0+cos35^0 * cos35^0-4 * \frac{1}{2}=
=sin^235^0+cos^235^0-2=1-2=-1