Giúp em những câu này với ạ!
a) \(\lim\limits_{x\to a} \dfrac{\sin x -\sin a}{x-a}\)
b) \(\lim\limits_{x\to \pi} \dfrac{1-\sin \dfrac{x}{2}}{\pi-x}\)
c) \(\lim\limits_{x\to \dfrac{\pi}{3}} \dfrac{\sin(x-\dfrac{\pi}{3})}{1-2\cos x}\)
d) \(\lim\limits_{x\to a} \dfrac{\tan^2 x - \tan^2 a}{\tan(x-a)}\)