Because the funeral is 1990 and this person is 100 years old,
So x >1990-100 =1890.
Namely 1890
According to x+n = n 2.
So n 2-n-x = 0.
X = N*(N- 1)
Between 1890 and 1990, it can be expressed as the product of two adjacent natural numbers, including:
43×44 = 1892
44×45 = 1980
That is, x = 1892 or 1980.
Because when x = 1980 and N=45, this is obviously not in line with the meaning of the question, so I omitted it.
Therefore, x = 1892, N = 44.
So this person was born in 1892.