In a triangle ABC, $2ca \sin \frac{A - B + C}{2}$ is equal to :

Question

( A ) $a^2 + b^2 - c^2$
( B ) $b^2 - c^2 - a^2$
( C ) $c^2 - a^2 - b^2$
( D ) $c^2 + a^2 - b^2$