根据这本书，大O的意思是：
f(n) = O(g(n)) means c · g(n) is an upper bound on f(n). Thus there exists some constant c such that f(n) is always ≤ c · g(n), for large enough n (i.e. , n ≥ n0 for some constant n0).
我无法理解下面的大 O 方程
3n2 − 100n + 6 = O(n2)，因为我选择 c = 3 并且 3n2 > 3n2 − 100n + 6；
3怎么能成为因数呢？在 3n2 − 100n + 6 中，如果我们去掉低阶项 -100n 和 6，3n2 和 3.n2 不是一样吗？如何解这个方程？
我将冒昧地稍微解释一下这个问题：
Why do
and
have the same asymptotic complexity.
为了做到这一点，定义应该是双向的。
let
Then for the inequality is always satisfied.
let
We have a parabola opened upwards, therefore there is again some after which the inequality is always satisfied.
