关于函数无穷大无穷小的阶的问题
Interpret and prove3 the following relations as x → x0 ∈ R:
O(f(x)) + O(g(x)) = O(|f(x)| + |g(x)|),
O(f(x))o(g(x)) = o(f(x))o(g(x)) = o(f(x)g(x)),
o(O(f(x)) = O(o(f(x)) = o(o(f(x))) = o(f(x))
如何证明这三个式子?