If φ = arccos(-5/13), then cos(φ) = -5/13. Since this is negative, you know φ is an angle that terminates either the second or third quadrant.
arctan(x) has a range of -π/2 < arctan(x) < π/2, which is to say that arctan(x) is an angle that terminates in either the first or fourth quadrant.
These quadrants don't overlap, so there is no solution to the equation.
