# Thread: need linear equation help

1. ## need linear equation help

F = (9/5)C +32
If (x + 10)C = xF, find x.

The answer is x = −62.5.
But how to work it out?

2. Originally Posted by Garp
F = (9/5)C +32
If (x + 10)C = xF, find x.

The answer is x = −62.5.
But how to work it out?
Since you have 3 variables and only 2 equations, you cannot solve for x. You need some additional information.

3. Originally Posted by alexmahone
Since you have 3 variables and only 2 equations, you cannot solve for x. You need some additional information.
Here's the whole thing.

The formula for converting degrees Celsius, C, to degrees Fahrenheit, F, is F = (9/5)C + 32.
a Convert 30◦F to Celsius.
b Convert 30◦C to Fahrenheit.
c If x◦C = x◦F find x.
d If (x + 10)◦C = x◦F find x.
e If 2x◦C = x◦F find the value of x. f If k◦F = (−3k)◦C find k.

4. Originally Posted by Garp
F = (9/5)C +32
If (x + 10)C = xF, find x.

The answer is x = −62.5.
But how to work it out?
$\displaystyle \frac{9}{5}(x+10)+32=x$

$\displaystyle \frac{9}{5}(x+10)=x-32$

$\displaystyle 9(x+10)=5x-160$

solve for x

5. it's not (x+10)C=xF, but (x + 10)◦C = x◦F

you've mixed up units and variables

so substitute (x+10) to C in and x to F for the given formula

it's not (x+10)C=xF, but (x + 10)◦C = x◦F

you've mixed up units and variables

so substitute (x+10) to C in and x to F for the given formula
Haha, forgive my stupidity. >.<

thanks for everyone that helped me!

7. Originally Posted by Garp
Haha, forgive my stupidity. >.<

thanks for everyone that helped me!
It's not stupidity, it's a subtle but important point.