I'm not sure he's right at all. I'd define any equation "a" which can be re-arranged to equation "b" to be equal ie. a==b They are the same thing. Thusly

I'm not sure he's right at all. I'd define any equation "a" which can be re-arranged to equation "b" to be equal ie. a==b They are the same thing. Thusly y=3x+2 is equal to 10y-20=30x is equal to 5y-15x=10 etc It's been a while since uni, but I don't remember any other mathematical definition of equations being considered equal. I guess the thought is something about what is being defined in terms of what (y= vs x=) but I don't think that's a meaningful distinction between two equations.