Limits and L'Hospital's Rule

1. L'Hospital's Rule 1 ${\textstyle \lim _{x\to 0}{f(x) \over g(x)}=lim_{x\to 0}{f'(x) \over g'(x)}}$
2. L'Hospital's Rule 2 ${\textstyle \lim _{x\to \infty }{f(x) \over g(x)}=lim_{x\to \infty }{f'(x) \over g'(x)}}$

there are some of the problems that can't use the L'Hospital's Rule such as:

Failed to parse (unknown function "\x"): {\textstyle \lim_{x\to \infty } {x + cos x \x}}