To find a positive and a negative angle coterminal<span> with a given </span>angle<span>, you can add and subtract if the </span>angle<span> is measured in degrees or if the </span>angle<span> is measured in radians</span>
∠1 = 50°
∠2=70°
If ∠3 is exterior ansgle with respect to ∠1 and ∠2, ∠3 must be ∠1+∠2 = 50°+70° =120°..Whereas, the interior angle with ∠3 will be 180°-120°=60°