For what value of [tex]$x$[/tex] is [tex]$\cos (x)=\sin \left(14^{\circ}\right)$[/tex], where [tex][tex]$0^{\circ}\ \textless \ x\ \textless \ 90^{\circ}$[/tex][/tex]?

A. [tex]$28^{\circ}$[/tex]
B. [tex]$31^{\circ}$[/tex]
C. [tex][tex]$14^{\circ}$[/tex][/tex]
D. [tex]$76^{\circ}$[/tex]



Answer :

To solve the problem of finding the value of [tex]\( x \)[/tex] such that [tex]\(\cos(x) = \sin(14^\circ)\)[/tex] within the range [tex]\(0^\circ < x < 90^\circ\)[/tex], we can use a fundamental trigonometric identity.

### Step-by-Step Solution:

1. Understanding the Trigonometric Identity:
- One of the fundamental trigonometric identities states that for any angle [tex]\(\theta\)[/tex]:
[tex]\[ \cos(\theta) = \sin(90^\circ - \theta) \][/tex]

2. Applying the Identity:
- In this problem, we need to find [tex]\( x \)[/tex] such that:
[tex]\[ \cos(x) = \sin(14^\circ) \][/tex]
- According to the identity stated above:
[tex]\[ \sin(14^\circ) = \cos(76^\circ) \][/tex]
- Therefore, we have:
[tex]\[ \cos(x) = \cos(76^\circ) \][/tex]

3. Equating the Angles:
- Since the cosine function is equal when their angles are equal (as [tex]\(0^\circ < x < 90^\circ\)[/tex]):
[tex]\[ x = 76^\circ \][/tex]

So, the value of [tex]\( x \)[/tex] that satisfies the equation [tex]\(\cos(x) = \sin(14^\circ)\)[/tex] within the given range is:
[tex]\[ \boxed{76^\circ} \][/tex]