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Make a line AB with a point O on it 
Draw 80° using protractor on that point 

Now, make a 180°arc on the that point.
Place the needle of the compass at the point of the Arc touching AB and the pencil tip at the 80°line.
keeping the compass as it is , place the compass needle on the point of the arc touching 80°line , and the mark the point touching the 180° arc and name it X

draw a line joining point O and X.
And congrats, u got twice angle 80° :D
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