Find the diagonal $ d_1 $ of a rhombus if side $a = 36$ and area $A = 9$.

$d_1 = 71.9996$

STEP 1: find height $ h $

To find height $ h $ use formula:

$$ A = a \cdot h $$

After substituting $ A = 9 $ and $ a = 36 $ we have:

$$ 9 = 36 \cdot h $$$$ h = \dfrac{ 9 }{ 36 } $$$$ h = \frac{ 1 }{ 4 } $$

STEP 2: find angle $ \alpha $

To find angle $ \alpha $ use formula:

$$ \sin \left( \alpha \right) = \dfrac{ h }{ a } $$

After substituting $ h = \frac{ 1 }{ 4 } $ and $ a = 36 $ we have:

$$ \sin \left( \alpha \right) = \dfrac{ \frac{ 1 }{ 4 } }{ 36 } $$ $$ \sin \left( \alpha \right) = \frac{ 1 }{ 144 } $$ $$ \alpha = \arcsin\left( \frac{ 1 }{ 144 } \right) $$ $$ \alpha = 0.3979^o $$

STEP 3: find diagonal $ d1 $

To find diagonal $ d1 $ use formula:

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

After substituting $ \alpha = 0.1989 $ and $ h = \frac{ 1 }{ 4 } $ we have:

$$ \sin \left( \frac{ 0.3979^o }{ 2 } \right) = \dfrac{ h }{ } $$ $$ \sin( 0.1989 ) = \dfrac{ \frac{ 1 }{ 4 } }{ d_1 } $$ $$ 0.0035 = \dfrac{ \frac{ 1 }{ 4 } }{ d_1 } $$ $$ d_1 = \dfrac{ \frac{ 1 }{ 4 } }{ 0.0035 } $$ $$ d_1 = 71.9996 $$

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