Greetings from Brasil...
See the attached figure. The smaller the θ angle, the smaller the AB side will be. If the angle θ = 90º, then AB = 25. As θ < 90, then AB < 25
5X - 10 < 25
5X < 25 + 10
X < 35/5
X < 7
The AB side can be neither zero nor negative. So
5X - 10 > 0
5X > 10
X > 10/5
X > 2
2 < X < 7
