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

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


Sagot :

To find the value of [tex]\( x \)[/tex] for which [tex]\(\cos (x)=\sin \left(14^{\circ}\right)\)[/tex], given that [tex]\(0^{\circ}
The co-function identity states that:
[tex]\[ \cos(x) = \sin(90^\circ - x) \][/tex]

Given [tex]\(\cos(x) = \sin(14^\circ)\)[/tex], we can set these equal and use the co-function identity to write:
[tex]\[ \sin(90^\circ - x) = \sin(14^\circ) \][/tex]

Since the sine function is periodic and one-to-one in the interval [tex]\(0^\circ < x < 90^\circ\)[/tex], we equate the arguments:
[tex]\[ 90^\circ - x = 14^\circ \][/tex]

Now, solve for [tex]\( x \)[/tex]:
[tex]\[ 90^\circ - x = 14^\circ \][/tex]

Subtract [tex]\(14^\circ\)[/tex] from both sides:
[tex]\[ 90^\circ - 14^\circ = x \][/tex]

Thus:
[tex]\[ x = 76^\circ \][/tex]

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