Octagon from rectangle

We cut the corners of a rectangular tablecloth with dimensions of 4 dm and 8 dm into isosceles triangles. Thus, the octagon formed had an area of 26 dm². How many dm² of tablecloth do we cut down?

Correct answer:

x =  6 dm²

Step-by-step explanation:

$$\begin{gathered} a=8\text{dm} \\ b=4\text{dm} \\ {S}_1=26{\text{dm}}^2 \\ {S}_2=a\cdot b=8\cdot 4=32{\text{dm}}^2 \\ x=S_2-S_1=32-26=6{\text{dm}}^2 \end{gathered}$$

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