Given:
Area of the rectangle is defined as
[tex]A(x)=3x^2+21x[/tex]
Width of the rectangle = 3x
Required: Length of the rectangle
Explanation:
The formula to find the area of a rectangle is
Area = Length x Width
Plug the given values into the formula.
[tex]\begin{gathered} 3x^2+21x=l\cdot3x \\ l=\frac{3x^2+21x}{3x} \\ =\frac{3x^2}{3x}+\frac{21x}{3x} \\ =x+7 \end{gathered}[/tex]
So, the length of the rectangle is x + 7.
Final Answer: The length of the rectangle is x+7.
