Write the expression as either the sine, cosine, or tangent of a single angle.

sin 57° cos 13° - cos 57° sin 13°

There exists a trigonometric identity which states that,
                  sin (A - B) = sin A cos B - cos A sin B
This is very similar to the given expression with A equal to 57° and B equal to 13°. The simplified form of the angle is,
                                 sin (57° - 13°) = sin 44°