To find diagonal $ d1 $ use formula:

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

After substituting $d_2 = 36\, \text{cm}$ and $a = 36\, \text{cm}$ we have:

$$ d_1 ^ {\,2} + \left( 36\, \text{cm} \right)^{2} = 4 \cdot \left( 36\, \text{cm} \right)^{2} $$ $$ d_1 ^ {\,2} + 1296\, \text{cm}^2 = = 5184\, \text{cm}^2 $$ $$ d_1 ^ {\,2} = = 5184\, \text{cm}^2 - 1296\, \text{cm}^2 $$ $$ d_1 ^ {\,2} = 3888\, \text{cm}^2 $$ $$ d_1 = \sqrt{ 3888\, \text{cm}^2 } $$$$ d_1 = 36 \sqrt{ 3 }\, \text{cm} $$

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