To find area $ A $ use formula:

$$ A = \dfrac{ a \cdot a \cdot \sin( \alpha ) }{ 1 } $$

After substituting $a = 11.3137\, \text{cm}$, $a = 11.3137\, \text{cm}$ and $\alpha = 45^o$ we have:

$$ A = \dfrac{ 11.3137\, \text{cm} \cdot 11.3137\, \text{cm} \cdot \sin( 45^o ) }{ 1 } $$ $$ A = \dfrac{ 11.3137\, \text{cm} \cdot 11.3137\, \text{cm} \cdot \frac{\sqrt{ 2 }}{ 2 } }{ 1 } $$ $$ A = \dfrac{ 128\, \text{cm}^2 \cdot \frac{\sqrt{ 2 }}{ 2 } }{ 1 } $$ $$ A = \dfrac{ 90.5097\, \text{cm}^2 }{ 1 } $$ $$ A \approx 90.5097\, \text{cm}^2 $$

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