## Intermediate Algebra (12th Edition)

$F=C=-40^{o}$
We start the with Celsius-to-Fahrenheit equation: $F=\frac{9}{5}C+32$ We wish to know when $F$ and $C$ are equal, so we set $F=C$ and solve for $C$: $C=\displaystyle \frac{9}{5}C+32$ $5C=5(\displaystyle \frac{9}{5}C+32)$ $5C=9C+5*32$ $5C=9C+160$ $-160=4C$ $4C=-160$ $C=-40^{o}$ Thus $F$ and $C$ are equal at $-40^{o}$ (this can be confirmed in the picture).