a; \(\lim\limits_{x\rightarrow-1}\dfrac{x^5+1}{x^3+1}\)
b; \(\lim\limits_{x\rightarrow a}\dfrac{x^n-a^n}{x-a}\)
c; \(\lim\limits_{x\rightarrow1}\dfrac{x+x^2+.............+x^n-n}{x-1}\)
d; \(\lim\limits_{x\rightarrow1}\dfrac{x^{100}-2x+1}{x^{50}-2x+1}\)