In Excel, the formula you type into a cell determines the value that will be displayed in that cell.
So, if you want to consider the formula to be the RHS of an equation, then you could just as well say that the value displayed in the cell is the LHS.
On the other hand, if you want to enter a formula for an equation into a cell, then the cell will display the "value" that equation. However, the value of an entire equation can only be TRUE, if the LHS and the RHS have the same value, or FALSE otherwise.
For instance, if you have values in the cells A1 and B1, the formula to determine if the values are equal is: = A1 = B1. Place this in C1.
If the value in A1 matches the value in B1, then C1 displays TRUE; otherwise, C1 displays false.