To find side $ a $ use Pythagorean Theorem:

$$ a^2 + b^2 = d^2 $$

After substituting $b = 0.049\, \text{cm}$ and $d = 0.054\, \text{cm}$ we have:

$$ a ^ {\,2} + \left( 0.049\, \text{cm} \right)^{2} = \left( 0.054\, \text{cm} \right)^{2} $$ $$ a ^ {\,2} = \left( 0.054\, \text{cm} \right)^{2} - \left( 0.049\, \text{cm} \right)^{2} $$ $$ a ^ {\,2} = 0.0029\, \text{cm}^2 - 0.0024\, \text{cm}^2 $$ $$ a ^ {\,2} = 0.0005\, \text{cm}^2 $$ $$ a = \sqrt{ 0.0005\, \text{cm}^2 } $$$$ a = 0.0227\, \text{cm} $$

Rectangle Calculator