The conjugate of the complex number a + bi is the complex number a - bi .  In other terms, it is the original complex number along the sign on the imaginary part changed.  Here are some instance of complex numbers and their conjugates.

complex number                  conjugate

3+ (½) i                              3 - (½) i

12 - 5i                               12+ 5i

1 - i                                     1+i

45i                                      45i

101                                     101

Note that the conjugate of a real number is only itself with no changes.