STEP 1: find angle $ \beta $
To find angle $ \beta $ use formula:
$$ \alpha + \beta = 90^o $$After substituting $ \alpha = 60^o $ we have:
$$ 60^o + \beta = 90^o $$ $$ \beta = 90^o - 60^o $$ $$ \beta = 30^o $$STEP 2: find diagonal $ d2 $
To find diagonal $ d2 $ use formula:
$$ \sin \left( \frac{ \beta }{ 2 } \right) = \dfrac{ h }{ d_2 } $$After substituting $ \beta = 15^o $ and $ h = 1 $ we have:
$$ \sin \left( \frac{ 30^o }{ 2 } \right) = \dfrac{ h }{ } $$ $$ \sin( 15^o ) = \dfrac{ 1 }{ d_2 } $$ $$ 0.2588 = \dfrac{ 1 }{ d_2 } $$ $$ d_2 = \dfrac{ 1 }{ 0.2588 } $$ $$ d_2 = 3.8637 $$