Well, the formula you use to convert a Fahrenheit temp
to a Celsius one is, as you said ...
F = 1.8C + 32 .
But if the Celsius and Fahrenheit temps are the same number,
then we can write 'C' in place of 'F', like this:
C = 1.8C + 32.
The rest is a piece o'cake.
Subtract 32 from each side: C - 32 = 1.8 C
Subtract 'C' from each side: - 32 = 0.8 C
Divide each side by 0.8 : C = -32/0.8
= -40° .
I happen to know that this is the correct solution,
but if I didn't, I'd check it, using the original formula
given in the question.
Find the Fahrenheit temp that's equivalent to -40°C .
F = 1.8 C + 32
= 1.8(-40) + 32
= -72 + 32
= -40 . yay !
