For [tex]\(0^{\circ} \leq x \ \textless \ 360^{\circ}\)[/tex], what are the solutions to [tex]\(\cos \left(\frac{x}{2}\right) - \sin (x) = 0\)[/tex]?

A. [tex]\(\{0^{\circ}, 60^{\circ}, 300^{\circ}\}\)[/tex]
B. [tex]\(\{0^{\circ}, 120^{\circ}, 240^{\circ}\}\)[/tex]
C. [tex]\(\{60^{\circ}, 180^{\circ}, 300^{\circ}\}\)[/tex]
D. [tex]\(\{120^{\circ}, 180^{\circ}, 240^{\circ}\}\)[/tex]



Answer :

To determine the solutions to the equation [tex]\(\cos\left(\frac{x}{2}\right) - \sin(x) = 0\)[/tex] for [tex]\(0^\circ \le x < 360^\circ\)[/tex], let's proceed step-by-step:

1. Rewrite the Equation:
We start with the given trigonometric equation:
[tex]\[ \cos\left(\frac{x}{2}\right) - \sin(x) = 0 \][/tex]
This can be rearranged to:
[tex]\[ \cos\left(\frac{x}{2}\right) = \sin(x) \][/tex]

2. Possible Solution Sets:
We'll consider different possible sets of angles within the given range ([tex]\(0^\circ\)[/tex] to [tex]\(360^\circ\)[/tex]).

3. Check the Given Options:
Our task is to determine which set of angles satisfies the equation.

a. Check [tex]\(\left\{0^\circ, 60^\circ, 300^\circ\right\}\)[/tex]:
- For [tex]\(x = 0^\circ\)[/tex]:
[tex]\[ \cos\left(\frac{0^\circ}{2}\right) = \cos(0^\circ) = 1 \][/tex]
[tex]\[ \sin(0^\circ) = 0 \][/tex]
[tex]\[ \cos(0^\circ) \neq \sin(0^\circ) \][/tex]
So, [tex]\(0^\circ\)[/tex] does not satisfy the equation.

b. Check [tex]\(\left\{0^\circ, 120^\circ, 240^\circ\right\}\)[/tex]:
- We already saw that [tex]\(0^\circ\)[/tex] doesn't satisfy the equation, so this set also does not satisfy the equation.

c. Check [tex]\(\left\{60^\circ, 180^\circ, 300^\circ\right\}\)[/tex]:
- For [tex]\(x = 60^\circ\)[/tex]:
[tex]\[ \cos\left(\frac{60^\circ}{2}\right) = \cos(30^\circ) = \frac{\sqrt{3}}{2} \][/tex]
[tex]\[ \sin(60^\circ) = \frac{\sqrt{3}}{2} \][/tex]
[tex]\[ \cos(30^\circ) = \sin(60^\circ) \][/tex]
So, [tex]\(60^\circ\)[/tex] satisfies the equation.
- For [tex]\(x = 180^\circ\)[/tex]:
[tex]\[ \cos\left(\frac{180^\circ}{2}\right) = \cos(90^\circ) = 0 \][/tex]
[tex]\[ \sin(180^\circ) = 0 \][/tex]
[tex]\[ \cos(90^\circ) = \sin(180^\circ) \][/tex]
So, [tex]\(180^\circ\)[/tex] satisfies the equation.
- For [tex]\(x = 300^\circ\)[/tex]:
[tex]\[ \cos\left(\frac{300^\circ}{2}\right) = \cos(150^\circ) = -\frac{\sqrt{3}}{2} \][/tex]
[tex]\[ \sin(300^\circ) = -\frac{\sqrt{3}}{2} \][/tex]
[tex]\[ \cos(150^\circ) = \sin(300^\circ) \][/tex]
So, [tex]\(300^\circ\)[/tex] satisfies the equation.

d. Check [tex]\(\left\{120^\circ, 180^\circ, 240^\circ\right\}\)[/tex]:
- For [tex]\(x = 120^\circ\)[/tex]:
[tex]\[ \cos\left(\frac{120^\circ}{2}\right) = \cos(60^\circ) = \frac{1}{2} \][/tex]
[tex]\[ \sin(120^\circ) = \frac{\sqrt{3}}{2} \][/tex]
[tex]\[ \cos(60^\circ) \neq \sin(120^\circ) \][/tex]
So, [tex]\(120^\circ\)[/tex] does not satisfy the equation.

Since [tex]\(\left\{60^\circ, 180^\circ, 300^\circ\right\}\)[/tex] is the set of angles that satisfies the equation, the correct answer is:

[tex]\(\boxed{\{60^\circ, 180^\circ, 300^\circ\}}\)[/tex]