Chegg这个网站怎么样

hbghlyj

一个商业网站. 例如一道射影几何题.
有一个中介微信public account可获得5次免费体验. 我用它查看了上面这道题:

发现所谓的"Expert anwer"只写了定义, 没有答题
而且是从Wikipedia Duality抄来的:

A projective plane $C$ may be defined axiomatically as an incidence structure, in terms of a set $P$ of points, a set $L$ of lines, and an incidence relation $I$ that determines which points lie on which lines. These sets can be used to define a plane dual structure.

Interchange the role of "points" and "lines" in
\[C = (P, L, I)\]
to obtain the dual structure
\[C^∗ = (L, P, I^∗),\]
where $I^∗$ is the converse relation of $I$.
$C^∗$ is also a projective plane, called the dual plane of $C$.

hbghlyj

時事新知：學生用AI抄答案成主流，線上教育平台Chegg股價崩99%