Let the four-digit number be a perfect square. By splitting it in the middle, we get two two-digit numbers and is a perfect square. By splitting in the middle, we get two two-digit numbers and is a perfect square. By splitting in the middle, we get two two-digit numbers and is a perfect square, and 9 times is the four-digit number which is also a perfect square. Find the four-digit numbers .
Solution
Solution: From the fact that 9 times is the four-digit number , and is also a perfect square, we have
From being the perfect square 1089, we have
Among the six four-digit numbers 1668, 6816, 6417, 1764, 3432, and 3234, only is a perfect square, so .
From being the perfect square 1764, we have
Upon inspection, only is a perfect square, so .
From being the perfect square 1849, we have , thus
Upon inspection, only 1156 and 1444 are perfect squares, so or 1444.
In summary, or ,
(Tian Yonghai, Suihua Educational Institute, Heilongjiang Province, 152054)
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