STEP 1: find side $ b $

To find side $ b $ use Pythagorean Theorem:

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

After substituting $a = 2\, \text{cm}$ and $d = 2.5\, \text{cm}$ we have:

$$ \left( 2\, \text{cm} \right)^{2} + b^2 = \left( 2.5\, \text{cm} \right)^{2} $$ $$ b^2 = \left( 2.5\, \text{cm} \right)^{2} - \left( 2\, \text{cm} \right)^{2} $$ $$ b^2 = 6.25\, \text{cm}^2 - 4\, \text{cm}^2 $$ $$ b^2 = 2.25\, \text{cm}^2 $$ $$ b = \sqrt{ 2.25\, \text{cm}^2 } $$$$ b = 1.5\, \text{cm} $$

STEP 2: find perimeter $ P $

To find perimeter $ P $ use formula:

$$ P = 2 a + 2 b $$

After substituting $a = 2\, \text{cm}$ and $b = 1.5\, \text{cm}$ we have:

$$ P = 2 \cdot 2\, \text{cm} + 2 \cdot 1.5\, \text{cm} $$ $$ P = 4\, \text{cm} + 3\, \text{cm} $$ $$ P = 7\, \text{cm} $$

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