Which expression is equivalent to [tex]\cos \left(103^{\circ}\right) \cos \left(54^{\circ}\right) - \sin \left(103^{\circ}\right) \sin \left(54^{\circ}\right)[/tex]?

A. [tex]\sin \left(49^{\circ}\right)[/tex]
B. [tex]\cos \left(49^{\circ}\right)[/tex]
C. [tex]\sin \left(157^{\circ}\right)[/tex]
D. [tex]\cos \left(157^{\circ}\right)[/tex]



Answer :

To determine which expression is equivalent to [tex]\(\cos(103^\circ) \cos(54^\circ) - \sin(103^\circ) \sin(54^\circ)\)[/tex], we can use the angle addition formula for cosine. The angle addition formula states that:

[tex]\[ \cos(A + B) = \cos(A)\cos(B) - \sin(A)\sin(B) \][/tex]

Given the expression [tex]\(\cos(103^\circ) \cos(54^\circ) - \sin(103^\circ) \sin(54^\circ)\)[/tex], we can recognize this as matching the form of [tex]\(\cos(A + B)\)[/tex] with [tex]\(A = 103^\circ\)[/tex] and [tex]\(B = 54^\circ\)[/tex]:

[tex]\[ \cos(103^\circ) \cos(54^\circ) - \sin(103^\circ) \sin(54^\circ) = \cos(103^\circ + 54^\circ) \][/tex]

Next, we add the angles:

[tex]\[ 103^\circ + 54^\circ = 157^\circ \][/tex]

Thus, the given expression simplifies to:

[tex]\[ \cos(157^\circ) \][/tex]

Therefore, the expression that is equivalent to [tex]\(\cos(103^\circ) \cos(54^\circ) - \sin(103^\circ) \sin(54^\circ)\)[/tex] is:

[tex]\[ \cos(157^\circ) \][/tex]

So the correct answer is:
[tex]\[ \cos(157^\circ) \][/tex]