Question Video: Identifying an Acute Angle | Nagwa Question Video: Identifying an Acute Angle | Nagwa

Question Video: Identifying an Acute Angle Mathematics • First Year of Preparatory School

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Which of the following is an acute angle? [A] Option (A) [B] Option (B) [C] Option (C) [D] Option (D)

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Video Transcript

Which of the following is an acute angle?

In this question, we need to identify which of the five given angles is an acute angle. We can do this by recalling that we say that an angle 𝐴𝐵𝐶 is acute if its measure is between zero and 90 degrees. We can see that of the five given options, only option (D) has a measure between these values. Thus, it is the only acute angle. We can also classify the other angles using their measures. First, we recall that angles with measure between 90 and 180 degrees are obtuse angles. So option (B) is an obtuse angle, since its measure is 120 degrees.

Next, we recall that an angle of measure greater than 180 degrees is a reflex angle. So option (A) is a reflex angle. We can also recall that an angle of measure 90 degrees is referred to as a right angle and that an angle of measure 180 degrees is called a straight angle.

It is also worth noting that we can answer this question without knowing the exact measures by noting that acute angles must have smaller measure than a right angle. So we can compare the size of the rotations to a quarter turn to see that only option (D) is an acute angle.

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