math
posted by john .
My math teacher wants us to prove that all of our answers are correct.
But how am I supposed to be able to prove stuff, like this, for example.
The directions want you to write out the words in to an equation.
Seven is the sum of X and 5.
so my answer is 7= x +5
How would I prove my answer?

Doesn't x = 2? Substitute 2 for x.
Doesn't 7 + 2 = 7? 
We're not supposed to figure out what the variable is.
The direction for the question was to write out the sentence in an equation 
The question wants you to figure out what number replaces X.
7 = x + 5
7 = ? + 5.
What number replaces x, or the questionmark? You're going to write:
x = (some digit, which is your answer)
Proving is easy. Just write
7 = x + 5 down again, but this time replacing x with your answer. 
Oh.
If it's any comfort, I have no idea how writing sentences embodying equations could be proven, either.