Find the diagonal $ d_1 $ of a rhombus if diagonal $d_2 = 9$ and angle $\beta = 36^o$.

$d_1 = 19.8242$

STEP 1: find angle $ \alpha $

To find angle $ \alpha $ use formula:

$$ \alpha + \beta = 90^o $$

After substituting $ \beta = 36^o $ we have:

$$ \alpha + 36^o = 90^o $$ $$ \alpha = 90^o - 36^o $$ $$ \alpha = 54^o $$

STEP 2: find diagonal $ d1 $

To find diagonal $ d1 $ use formula:

$$ \sin \left( \frac{ \alpha }{ 2 } \right) = \dfrac{ d_2 }{ d_1 } $$

After substituting $ \alpha = 27^o $ and $ d_2 = 9 $ we have:

$$ \sin \left( \frac{ 54^o }{ 2 } \right) = \dfrac{ d_2 }{ } $$ $$ \sin( 27^o ) = \dfrac{ 9 }{ d_1 } $$ $$ 0.454 = \dfrac{ 9 }{ d_1 } $$ $$ d_1 = \dfrac{ 9 }{ 0.454 } $$ $$ d_1 = 19.8242 $$

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