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Find the value of $a$ and the value of $b$, and give a geometrical reason for each answer.
Mathematics 0580 · IGCSE · Angles
Angles — practice question
A straight line crosses two parallel lines. At the upper crossing, the angle shown is $58^\circ$. At the lower crossing, the angles are labelled $a^\circ$ and $b^\circ$. The diagram is not drawn to scale.