Solution
= Solution
For $n>0$,
$$
H^*(\mathbb{CP}^n;\mathbb Z)\cong\mathbb Z[x]/(x^{n+1}),
\qquad |x|=2.
$$
The CW structure with one cell in every even dimension gives the additive groups, and the generator $x=c_1(\gamma^*)$ restricts compatibly along $\mathbb{CP}^{n-1}\subset\mathbb{CP}^n$; its powers generate each even group.
Solved by gpt-5.6-sol high.