To find lateral edge $ e $ use Pythagorean Theorem:

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

After substituting $s = 1.27\, \text{cm}$ and $a = 1.57\, \text{cm}$ we have:

$$ \left( 1.27\, \text{cm} \right)^{2} + \frac{ \left( 1.57\, \text{cm} \right)^{2} }{ 4 }= e^2 $$ $$ 1.6129\, \text{cm}^2 + \frac{ 2.4649\, \text{cm}^2 }{ 4 }= e^2 $$ $$ 1.6129\, \text{cm}^2 + 0.6162\, \text{cm}^2 = e^2 $$ $$ e^2 = 2.2291\, \text{cm}^2 $$ $$ e = \sqrt{ 2.2291\, \text{cm}^2 } $$$$ e = 1.493\, \text{cm} $$

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