Mark the statements that are true.

A. An angle that measures [tex]\frac{4 \pi}{3}[/tex] is a reflex angle.
B. An angle that measures [tex]300^{\circ}[/tex] is an obtuse angle.
C. An acute angle measures less than [tex]\frac{\pi}{2}[/tex].
D. An angle that measures [tex]65^{\circ}[/tex] is an acute angle.



Answer :

Let's examine each of the statements to determine which ones are true.

### Statement A:
An angle that measures [tex]\(\frac{4 \pi}{3}\)[/tex] is a reflex angle.

A reflex angle is an angle that is greater than [tex]\(180^\circ\)[/tex] but less than [tex]\(360^\circ\)[/tex]. To convert radians to degrees, we use the conversion factor [tex]\(180^\circ = \pi\)[/tex] radians.

[tex]\[ \frac{4 \pi}{3} \text{ radians} \times \frac{180^\circ}{\pi} = \frac{4 \times 180^\circ}{3} = 240^\circ \][/tex]

Since [tex]\(240^\circ\)[/tex] is greater than [tex]\(180^\circ\)[/tex] and less than [tex]\(360^\circ\)[/tex], [tex]\(\frac{4 \pi}{3}\)[/tex] radians is indeed a reflex angle.

### Conclusion:
Statement A is true.

### Statement B:
An angle that measures [tex]\(300^{\circ}\)[/tex] is an obtuse angle.

An obtuse angle is an angle that is greater than [tex]\(90^\circ\)[/tex] but less than [tex]\(180^\circ\)[/tex].

Since [tex]\(300^\circ\)[/tex] is greater than [tex]\(180^\circ\)[/tex], it cannot be an obtuse angle. It is instead a reflex angle as it is between [tex]\(180^\circ\)[/tex] and [tex]\(360^\circ\)[/tex].

### Conclusion:
Statement B is false.

### Statement C:
An acute angle measures less than [tex]\(\frac{\pi}{2}\)[/tex].

An acute angle is defined as an angle that is less than [tex]\(90^\circ\)[/tex]. We know that [tex]\(90^\circ\)[/tex] is equal to [tex]\(\frac{\pi}{2}\)[/tex] radians.

[tex]\[ \frac{\pi}{2} \times \frac{180^\circ}{\pi} = 90^\circ \][/tex]

Since [tex]\(90^\circ\)[/tex] is equal to [tex]\(\frac{\pi}{2}\)[/tex] radians and an acute angle is less than this, it confirms the definition correctly.

### Conclusion:
Statement C is true.

### Statement D:
An angle that measures [tex]\(65^{\circ}\)[/tex] is an acute angle.

As stated earlier, an acute angle is an angle that is less than [tex]\(90^\circ\)[/tex].

Since [tex]\(65^\circ\)[/tex] is less than [tex]\(90^\circ\)[/tex], it is indeed an acute angle.

### Conclusion:
Statement D is true.

### Summary
After evaluating all the statements:
- Statement A is true.
- Statement B is false.
- Statement C is true.
- Statement D is true.

Therefore, the true statements are:
[tex]\[ \boxed{A \text{ and } D} \][/tex]