Square

If the length of the sides of the square we decrease by 25% decrease the content area of 28 cm². Determine the side length of the original square.

Correct result:

a =  8 cm

Solution:

$$\begin{gathered} a^2-((1-25\mathrm{/}100)a{)}^2=28 \\ {8}^2-((1-25\mathrm{/}100)8{)}^2=28 \\ a=a_1=8=8\text{ cm} \end{gathered}$$

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