[ Unusual Constructions (Miscellaneous). ] [ Measuring the lengths of segments and measures of angles. Adjacent angles. $]$

There is an angle ruler with an angle of $70^{\circ}$. How can you construct an angle of $40^{\circ}$ with it?

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First method. $40^{\circ}=180^{\circ}-2 \cdot 70^{\circ}$.

Second method. If one angle of the triangle is $70^{\circ}$, then the second one is $20^{\circ} .40^{\circ}=2 \cdot 20^{\circ}$.