Giải bởi Vietjack
Hướng dẫn giải:
Ta có \(\widehat F = 180^\circ - \left( {\widehat D + \widehat E} \right) = 180^\circ - 30^\circ = 150^\circ \).
Do đó sinF = sin150° = sin(180° − 30°) = sin30° = \(\frac{1}{2}\);
cosF = cos150° = cos(180° − 30°)= − cos30° = \( - \frac{{\sqrt 3 }}{2}\);
tanF = \(\frac{{\sin 150^\circ }}{{\cos 150^\circ }} = \frac{{\frac{1}{2}}}{{ - \frac{{\sqrt 3 }}{2}}} = - \frac{{\sqrt 3 }}{3}\);
cotF = \(\frac{{cos150^\circ }}{{\sin 150^\circ }} = \frac{{ - \frac{{\sqrt 3 }}{2}}}{{\frac{1}{2}}}\)= \( - \sqrt 3 \).
