## Fahrenheit To Celsius

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I have heard that the normal body temperature of a human is 98.6 F. That seems unrealistically accurate, to me. Don't people vary a lot? Anyway, I was wondering, what is that temperature in degrees Celsius? But I can't remember the conversion formula.

It's something like C=xF+y, a linear equation in other words. And we know that 0 C=32 F (freezing), and 100 C=212 F (boiling). That should be enough to find x and y:

```    0 =  32x+y
100 = 212x+y
```

Two equations, two unknowns. There are several ways to solve this. Here's one way:

```    y = -32x
100 = 212x-32x
100 = 180x
x = 5/9
y = (-32)(5/9)
```

Substituting back in to the original equation:

```    C = xF+y
C = (5/9)F - (5/9)32
C = (5/9)(F-32)
```

That looks familiar. And 98.6 F=37 C. Now that doesn't look unrealistically accurate. I'll bet we got our 98.6 F from 37 C.

We can take that equation, C=(5/9)(F-32), and solve for F:

```    F = (9/5)C + 32
```

That's also familiar.

Apparently, Galileo invented the thermometer (several kinds which depended on the expansion and contraction of gasses). Celsius evidently invented the mercury thermometer, which we are familiar with. He also invented the Celsius temperature scale, which we called Centigrade until recently. Fahrenheit was a scientist whose fame rests mainly on the temperature scale that he invented.