Step-by-step explanation:

A+B+C=π,

∴A/2+B/2+C/2=π/2

∴tan(

2

A

+

2

B

+

2

C

)=tan

2

π

=∞.

or

1−S

2

S

1

−S

3

=∞

∴1−S

2

=0 or S

2

=1

or tan

2

A

tan

2

B

+tan

2

B

tan

2

C

+tan

2

C

tan

2

A

=1.