STEP 1: find side $ a $

To find side $ a $ use formula:

$$ h = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$

After substituting $h = 9\, \text{cm}$ we have:

$$ 9\, \text{cm} = \dfrac{ \sqrt{ 3 } \cdot a }{ 2 } $$ $$ \sqrt{ 3 } \cdot a = 9\, \text{cm} \cdot 2 $$ $$ \sqrt{ 3 } \cdot a = 18\, \text{cm} $$ $$ a = \dfrac{ 18\, \text{cm} }{ \sqrt{ 3 } } $$ $$ a = 6 \sqrt{ 3 }\, \text{cm} $$

STEP 2: find lateral $ AL $

To find lateral $ AL $ use formula:

$$ AL = 3 \cdot a \cdot l $$

After substituting $a = 6 \sqrt{ 3 }\, \text{cm}$ and $l = 26\, \text{cm}$ we have:

$$ AL = 18 \sqrt{ 3 }\, \text{cm} \cdot 26\, \text{cm} $$$$ AL = 468 \sqrt{ 3 }\, \text{cm}^2 $$

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