Rectangle

The length of the rectangle is 12 cm greater than 3 times its width. What dimensions and area this rectangle has if ts circumference is 104 cm.

Correct answer:

a =  42 cm
b =  10 cm
S =  420 cm²

Step-by-step explanation:

$$\begin{gathered} o=104\text{ cm } \\ 2(a+b)=o \\ a=12+3b \\ 2(a+b)=104 \\ a=12+3b \\ 2\cdot (a+b)=104 \\ a=12+3\cdot b \\ 2a+2b=104 \\ a-3b=12 \\ a=42=42\text{ cm } \\ b=10 \end{gathered}$$

$S=a\cdot b=42\cdot 10=420{\text{cm}}^2$

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