Tính:

a) sin(– 675°);

b) \(\tan \frac{{15\pi }}{4}\).

Lời giải:

Ta có:

a) sin(– 675°) = sin(45° – 2 . 360°) = sin 45° = \(\frac{{\sqrt 2 }}{2}\).

b) \(\tan \frac{{15\pi }}{4} = \tan \left( { - \frac{\pi }{4} + 4\pi } \right) = \tan \left( { - \frac{\pi }{4}} \right) = - \tan \frac{\pi }{4} = - 1\).