a) x + 3 + x + 4 = 2x + 7
2x + 7 = 2x + 7 (By simplification)[\ any value given to 'x' always satisfies the equation]
Similarly,b) (3a + 4) + 2 (a - 1) = 5a + 2
i.e., 5a + 2 = 5a + 2 (By simplification)[\ any value given to 'a' always satisfies the equation]
The two expressions (LHS and RHS) are always equal for any value we give to the variable. Equations that are true for any value of the variable are called identical equations or briefly an identity.