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

A. [tex]$31^{\circ}$[/tex]

B. [tex]$76^{\circ}$[/tex]

C. [tex][tex]$14^{\circ}$[/tex][/tex]

D. [tex]$28^{\circ}$[/tex]



Answer :

To find the value of [tex]\( x \)[/tex] for which [tex]\(\cos(x) = \sin(14^\circ)\)[/tex] within the interval [tex]\(0^\circ < x < 90^\circ\)[/tex], we can use the complementary angle identity in trigonometry.

Recall the complementary angle identity:
[tex]\[ \sin(90^\circ - \theta) = \cos(\theta) \][/tex]

We can rewrite [tex]\(\cos(x)\)[/tex] by using the fact that:
[tex]\[ \cos(x) = \sin(90^\circ - x) \][/tex]

Given in the question:
[tex]\[ \cos(x) = \sin(14^\circ) \][/tex]

From the complementary angle identity, we can equate:
[tex]\[ \sin(90^\circ - x) = \sin(14^\circ) \][/tex]

For the sine function, one key property is that if [tex]\(\sin(A) = \sin(B)\)[/tex], then [tex]\( A \)[/tex] can be equal to [tex]\( B \)[/tex] or [tex]\( 180^\circ - B \)[/tex].

But since [tex]\(0^\circ < x < 90^\circ\)[/tex], it is sufficient to consider only the direct equality due to the range restriction:
[tex]\[ 90^\circ - x = 14^\circ \][/tex]

Solving for [tex]\( x \)[/tex], we get:
[tex]\[ 90^\circ - 14^\circ = x \][/tex]
[tex]\[ x = 76^\circ \][/tex]

Thus, the value of [tex]\( x \)[/tex] is:
[tex]\[ \boxed{76^\circ} \][/tex]