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Simplify the expression:
[tex]\[ \cos^4(12\theta) - \sin^4(12\theta) = \cos(24\theta) \][/tex]


Sagot :

To simplify the expression [tex]\(\cos^4(12\theta) - \sin^4(12\theta)\)[/tex] and show that it is equivalent to [tex]\(\cos(24\theta)\)[/tex], we can follow these steps:

1. Identify Trigonometric Identities and Patterns:
We have the expression [tex]\(\cos^4(12\theta) - \sin^4(12\theta)\)[/tex]. Notice that this can be written as a difference of squares:
[tex]\[ \cos^4(12\theta) - \sin^4(12\theta) = (\cos^2(12\theta))^2 - (\sin^2(12\theta))^2. \][/tex]

2. Apply the Difference of Squares Formula:
Recall the difference of squares formula: [tex]\(a^2 - b^2 = (a + b)(a - b)\)[/tex]. Here, [tex]\(a = \cos^2(12\theta)\)[/tex] and [tex]\(b = \sin^2(12\theta)\)[/tex]. Applying this, we get:
[tex]\[ (\cos^2(12\theta))^2 - (\sin^2(12\theta))^2 = (\cos^2(12\theta) + \sin^2(12\theta))(\cos^2(12\theta) - \sin^2(12\theta)). \][/tex]

3. Simplify Using Known Identities:
We know from the Pythagorean identity that:
[tex]\[ \cos^2(12\theta) + \sin^2(12\theta) = 1. \][/tex]
Substituting this into our expression, we get:
[tex]\[ 1 \cdot (\cos^2(12\theta) - \sin^2(12\theta)) = \cos^2(12\theta) - \sin^2(12\theta). \][/tex]

4. Use the Double Angle Formula:
The last step involves recognizing that [tex]\(\cos^2(12\theta) - \sin^2(12\theta)\)[/tex] is a known trigonometric identity for the cosine of a double angle. Specifically,
[tex]\[ \cos(2A) = \cos^2(A) - \sin^2(A). \][/tex]
In our case, [tex]\(A\)[/tex] is [tex]\(12\theta\)[/tex]. Hence,
[tex]\[ \cos^2(12\theta) - \sin^2(12\theta) = \cos(24\theta). \][/tex]

Therefore, we have shown that:
[tex]\[ \cos^4(12\theta) - \sin^4(12\theta) = \cos(24\theta). \][/tex]

This completes the proof and shows the equivalence as required.