40°, 50° and 90°
the sum of the angles in a triangle = 180°
sum the parts of the ratio : 4 + 5 + 9 = 18 parts
divide 180 by 18 to obtain 1 part
= 10° ← 1 part
4 parts = 4 × 10 = 40°
5 parts = 5 × 10 = 50°
9 parts = 9 × 10 = 90°
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= 10° ← 1 part