NoblePenguin
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Please prove the following trigonometric identity.

[tex]\cos^2(5x)-\sin^2(5x)=\cos(10x)[/tex]

Sagot :

xKelvin

Answer:

See Below.

Step-by-step explanation:

We want to verify the trigonometric identity:

[tex]\cos^2(5x)-\sin^2(5x)=\cos(10x)[/tex]

For simplicity, we can let u = 5x. Therefore, by substitution, we acquire:

[tex]\cos^2(u)-\sin^2(u)[/tex]

Recall the double-angle identity formula(s) for cosine:

[tex]\displaystyle \begin{aligned} \cos(2x)&=\cos^2(x)-\sin^2(x)\\&=2\cos^2(x)-1\\&=1-2\sin^2(x)\end{aligned}[/tex]

Therefore, our identity becomes:

[tex]=\cos(2u)[/tex]

Back-substitute:

[tex]=\cos(2(5x))=\cos(10x)\stackrel{\checkmark}{=}\cos(10x)[/tex]

Hence proven.

abhi569

cos²A - sin²A = cos2A, this is a general indentity where A can have any random value x/2, y/3, 1/8, 8, 9 etc.

Replacing A with 5x:

=> cos²(5x) - sin²(5x) = cos²(10x)

Moreover,

cos(A + B) = cosAcosB - sinAsinB.

When A = B,

cos(A + A) = cosAcosA - sinAsinA

cos2A = cos²A - sin²A

You can do the same with 5x.

cos(10x) = cos(5x + 5x)

cos(10x) = cos(5x)cos(5x) - sin(5x)sin(5x)

cos(10x) = cos²(5x) - sin²(5x)

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