Let the common factor be x.
4x + 5x = 90°
9x = 90°
x = 10°
Angles were 4x and 5x.
4x = 4 * 10 = 40°
5x = 5 * 10 = 50°
Hence, two complementary angles which are in the ratio 4:5 are 40° and 50°.
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