Răspuns:
a) x = (90-x)/2 => 2x = 90-x => 3x = 90 => x = 30°
b) x = (180-x)/3 => 3x = 180-x => 4x = 180 => x = 45°
c) x/(90-x) = 2/7 => 7x = 180-2x => 9x = 180 => x = 20°
d) x/(90-x) = 4/5 => 5x = 360-4x => 9x = 360 => x = 40°
e) x-(90-x)=15 => 2x=90+15 => 2x = 105 => x = 52°30'