If [tex]\(0 \ \textless \ b \leq 90\)[/tex] and [tex]\(\cos (11b + 2) = \sin (12b - 4)\)[/tex], what is the value of [tex]\(b\)[/tex]?

A. [tex]\(b = 3\)[/tex]
B. [tex]\(b = 4\)[/tex]
C. [tex]\(b = 5\)[/tex]
D. [tex]\(b = 6\)[/tex]



Answer :

To solve the equation [tex]\(\cos(11b + 2) = \sin(12b - 4)\)[/tex], we can use a trigonometric identity. The identity that relates cosine and sine is given by:

[tex]\[ \cos(x) = \sin(90^\circ - x) \][/tex]

Applying this identity, we can rewrite the original equation [tex]\(\cos(11b + 2)\)[/tex] as:

[tex]\[ \cos(11b + 2) = \sin(90^\circ - (11b + 2)) \][/tex]

So, the given equation [tex]\(\cos(11b + 2) = \sin(12b - 4)\)[/tex] can be rewritten using this identity as:

[tex]\[ \sin(90 - (11b + 2)) = \sin(12b - 4) \][/tex]

Simplify the argument of the sine function on the left side:

[tex]\[ \sin(90 - 11b - 2) = \sin(12b - 4) \][/tex]

[tex]\[ \sin(88 - 11b) = \sin(12b - 4) \][/tex]

For the sine of two angles to be equal, the angles themselves must either be equal, or they must sum to [tex]\(180^\circ\)[/tex] given the periodic nature of the sine function. Therefore, we have:

[tex]\[ 88 - 11b = 12b - 4 \][/tex]

or

[tex]\[ 88 - 11b = 180^\circ - (12b - 4) \][/tex]

Let’s solve the first equation:

[tex]\[ 88 - 11b = 12b - 4 \][/tex]

Move all terms involving [tex]\(b\)[/tex] to one side and constants to the other:

[tex]\[ 88 + 4 = 12b + 11b \][/tex]

[tex]\[ 92 = 23b \][/tex]

Divide both sides by 23:

[tex]\[ b = \frac{92}{23} \][/tex]

Simplify:

[tex]\[ b = 4 \][/tex]

Therefore, the value of [tex]\(b\)[/tex] is [tex]\( \boxed{4} \)[/tex].

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