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Acute, obtuse and right angle


We can classify an angle as acute, obtuse, or straight.

  • Acute angle is the angle whose measurement is less than 90 °. Example:

  • Obtuse angle is the angle whose measurement is greater than 90º. Example:

  • Straight angle is the angle whose measurement is 90º. Example:

Perpendicular lines

The straight r and s of the figure below are competing and form four right angles to each other.

We say that lines r and s are perpendicular and we indicate:

Note:

Two competing lines that do not form right angles to each other are called oblique. Example:

Next: Complementary Angles