a^2+b^2
=(n^2-1)^2+(2n)^2
=n^4-2n^2+1+4n^2
=n^4+2n^2+1
=(n2+1)^2
=c^2
a^2+b^2=c^2,
根据勾股定理,这三角形是直角三角形.
并且C是直角