Which of the following is an example of an open equation? 5x + 7 = 12 , 12 + (-8) = 4 , 25 = 5 (5) , 8 + 0 =8 (math)

An open equation is an equation that contain one or more unknow variables.

And that/those variable(s) can be found by solving the equation that make the equation true.

A variable is an English alphabet.

For example, a,b, x, y,z etc.

A variable represents a unknow value for a particular quantity.

In the given options 5x + 7 = 12 , 12 + (-8) = 4 , 25 = 5 (5) , 8 + 0 =8 .

In first option, we have unknow variable x is there.

But in all other options we don't value any variable.

Therefore, all other options can't be open equation.

So, final answer is 5x + 7 = 12 is the only open equation in given options.