The equation \( x + 1 = x + 1 \) is always true for any value of \( x \).
In the expression "\( ? + 1 = ? + 1 \)", you can substitute any variable or number in place of \( ? \). It will also be true and remains a valid equation.
In essence, both statements are equalities that hold for any value. For example, if you replace \( ? \) with \( y \), it becomes \( y + 1 = y + 1 \), which is also always true.
So, any value can be substituted for \( ? \) and the equation will remain valid.