Question

A wire of length r feet is bent into a rectangle whose width is 2 times its height. Write the area A of the rectangle as a function of the wire's leng

Solid Geometry
ANSWERED
asked 2021-05-09
A wire of length r feet is bent into a rectangle whose width is 2 times its height. Write the area A of the rectangle as a function of the wire's length r. Write the wire's length r as a function of the area A of the rectangle (note A not a).

Answers (2)

2021-05-10

The length of the wire is the perimeter of the rectangle with width ww and height hh:
\(2w+2h=r\)
Given that the width is 2 times its height, \(w=2h\), we write: \(2(2h)+2h=r\)
\(4h+2h=r\)
\(6h=r\)
\(\displaystyle{h}=\frac{{r}}{{6}}\)
which follows that:
\(\displaystyle{w}={2}⋅\frac{{r}}{{6}}=\frac{{r}}{{3}}\)
The area of the rectangle is:
\(A=wh\)
In terms of r,
\(\displaystyle{A}={r}{3}⋅{r}{6}\)
\(\displaystyle{A}=\frac{{r}^{{2}}}{{18}}\)
Solve for rr in terms of AA:
\(\displaystyle{18}{A}={r}^{{2}}\)
\(\displaystyle\sqrt{18A}={r}\)
or
\(\displaystyle{r}={3}\sqrt{2A}\)

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2021-08-11

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