1. the area of rectangular

the area of this rectangular (the small one )

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2. Re: the area of rectangular

$A=60 \cdot 40-2\cdot\left(\frac{(60-x)(40-x)}{2}+\frac{x\cdot x}{2}\right)$

$A= 60\cdot 40-(2400-100x+x^2+x^2)$

$A=100x-2x^2 ~\text{ where }~x\in(0,40)$