STEP 1: find diagonal $ d2 $
To find diagonal $ d2 $ use formula:
$$ d_1^2 + d_2^2 = 4 \cdot a^2 $$After substituting $d_1 = 25.2\, \text{cm}$ and $a = 18.5\, \text{cm}$ we have:
$$ \left( 25.2\, \text{cm} \right)^{2} + d_2^2 = 4 \cdot \left( 18.5\, \text{cm} \right)^{2} $$ $$ 635.04\, \text{cm}^2 + d_2^2 = 1369\, \text{cm}^2 $$ $$ d_2^2 = 1369\, \text{cm}^2 - 635.04\, \text{cm}^2 $$ $$ d_2^2 = 733.96\, \text{cm}^2 $$ $$ d_2 = \sqrt{ 733.96\, \text{cm}^2 } $$$$ d_2 = 27.0917\, \text{cm} $$STEP 2: find angle $ \alpha $
To find angle $ \alpha $ use formula:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ d_2 }{ d_1 } $$After substituting $d_2 = 27.0917\, \text{cm}$ and $d_1 = 25.2\, \text{cm}$ we have:
$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ 27.0917\, \text{cm} }{ 25.2\, \text{cm} } $$ $$ \sin \left( \frac{ \alpha }{ 2 } \right) = 1.0751 $$ $$ \frac{ \alpha }{ 2 } = \arcsin\left( 1.0751 \right) $$$ \arcsin(1.075) $ is not defined $ \Longrightarrow $ The problem has no solution.