To find lateral edge $ e $ use Pythagorean Theorem:

$$ s^2 + \frac{ a^2 }{ 4 } = e^2 $$

After substituting $s = 0.809\, \text{cm}$ and $a = 1\, \text{cm}$ we have:

$$ \left( 0.809\, \text{cm} \right)^{2} + \frac{ \left( 1\, \text{cm} \right)^{2} }{ 4 }= e^2 $$ $$ 0.6545\, \text{cm}^2 + \frac{ 1\, \text{cm}^2 }{ 4 }= e^2 $$ $$ 0.6545\, \text{cm}^2 + \frac{ 1 }{ 4 }\, \text{cm}^2 = e^2 $$ $$ e^2 = 0.9045\, \text{cm}^2 $$ $$ e = \sqrt{ 0.9045\, \text{cm}^2 } $$$$ e = 0.951\, \text{cm} $$

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