We studied that

1 revolution = Full angle

1/4 revolution = Right Angle

1/2 revolution = Straight angle

Now,

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Acute angle
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is less than right angle.

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Other examples are
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Obtuse Angles
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Obtuse angle is angle greater than a right angle but smaller than a straight angle.

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Other examples are
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Reflex Angles
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Reflex angle is greater than a straight angle

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Other examples are
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