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Definition 51.1 Primary & Middle School Mathematics · অধ্যায় 51 — Triangles and Angles

• Two angles are complementary when their measures add up to $90^\circ$, supplementary when they add up to $180^\circ$.
• When two lines cross, the angles facing each other across the crossing point are vertically opposite.
• When a line crosses two other lines, angles located in the same position at each crossing are corresponding angles; angles between the two lines on opposite sides of the crossing line are alternate angles.

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