two angles are complementary if they add up to 90 degrees

let the angles be x and y

one angle is twice the other angle

x = 2y

x and y are complementary

x + y = 90

by solving the system of equations

x = 2y

x + y = 90

we find

x = 60 degrees

y = 30 degrees

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the two angles are 30 and 60 degrees.