you energy

It's not incorrect, it's just the way engineers do equations.

e = mc

π = 3

g = 10 m/s²

So close

And m represents mass, not matter. Matter has mass, but that doesn't mean it is mass.

In natural units, where c = ħ =1, both statements are equally true. But then, the whole premise is lost because in these units, E = m (for stationary bodies).