Solve 4 sinx + 9 cosx=0 for 0° ​

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°