Mean triangles

In a triangle ABC, a, b and A are given to you (i.e. they're constant) with b>a.(Length of the side opposite to A is $a$ ). $c_1$ and $c_2$ are two possible values of the third side c. If $S_1$ and $S_2$ denote the areas of the two triangles with sides $a,b,c_1$ and $a,b,c_2$ respectively, which of the following statements are correct?

1.) Arithmetic Mean of $S_1$ and $S_2$ is $\frac {b^2 \sin 2A}{4}$

2.) Geometric Mean of $S_1$ and $S_2$ is $\frac {b \sin A}{2}$

3.) Harmonic Mean of $S_1$ and $S_2$ is $(\frac {b^2-a^2}{2}) \tan A$

4.) $|S_1-S_2|=b \sin A\sqrt {a^2-b^2\sin A}$

Give your answer as the concatenation of the serial numbers of the statements which are correct. (For example, if 1.), 2.) and 3.) are correct, give your answer as 123)