Question

John is going on a trip and the country he is traveling to uses the Celsius scale. He is curious about converting Celsius temperatures to Fahrenheit. John determines 68°F is equivalent to 20°C and 86°F is equivalent to 30°C.
Which function models the relationship between Fahrenheit and Celsius?

Answer 1

Answer:

The answer is 9/5c + 32

Answer 2

Answer:

$f(x)=\dfrac{9}{5}x+32$ converts Celsius to Fahrenheit.

$g(x)=\dfrac{5(x-32)}{9}$ converts Fahrenheit to Celsius.

Step-by-step explanation:

Write given data in the table

$\begin{array}{cc}x&f(x)\\^{\circ}\text{C}&^{\circ}\text{F}\\20&68\\30&86\end{array}$

Let the expression for the function be

$f(x)=ax+b$

Note, that this equation is linear equation and it is well-known fact that the Celsius to Fahrenheit dependence is linear.

Substitute corresponding values into this expression:

$68=20a+b\\ \\86=30a+b$

Subtract these two equations:

$86-68=30a-20a\\ \\10a=18\\ \\a=\dfrac{9}{5}$

Substitute it into the first equation:

$68=20\cdot \dfrac{9}{5}+b\Rightarrow b=68-36=32$

So,

$f(x)=\dfrac{9}{5}x+32$

This is the function which converts Celsius to Fahrenheit.

And function

$g(x)=\dfrac{5(x-32)}{9}$ converts Fahrenheit to Celsius.