4 sin(x) + 9 cos(x) = 0
4 sin(x) = -9 cos(x)
tan(x) = -9/4
x = arctan(-9/4) + nπ … … … (in radians)
or
x = arctan(-9/4) + 180n ° … … … (in degrees)
where n is any integer.
I'm guessing you're solving for x over some domain, probably 0° ≤ x < 360°. In that case, you would have two solutions for n = 1 and n = 2 of
x ≈ 113.96° and x ≈ 293.96°
