To find side $ a $ use formula:

$$ d_1^2 + d_2^2 = 4 \cdot a^2 $$

After substituting $d_1 = 249.7\, \text{cm}$ and $d_2 = 251.2\, \text{cm}$ we have:

$$ \left( 249.7\, \text{cm} \right)^{2} + \left( 251.2\, \text{cm} \right)^{2} = 4 \cdot a^2 $$ $$ 62350.09\, \text{cm}^2 + 63101.44\, \text{cm}^2 = 4 \cdot a^2 $$ $$ 4 \cdot a^2 = 125451.53\, \text{cm}^2 $$ $$ a^2 = \frac{ 125451.53\, \text{cm}^2 }{ 4 } $$ $$ a^2 = 31362.8825\, \text{cm}^2 $$ $$ a = \sqrt{ 31362.8825\, \text{cm}^2 } $$$$ a = 177.0957\, \text{cm} $$

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