If [tex]$0 \ \textless \ A \ \textless \ B \ \textless \ \frac{\pi}{4}$[/tex], [tex]\sin (A + B) = \frac{24}{25}[/tex], and [tex]\cos (A - B) = \frac{4}{5}[/tex], find the value of [tex]\tan 2A[/tex].



Answer :

To solve for [tex]\(\tan(2A)\)[/tex] given [tex]\(\sin(A+B) = \frac{24}{25}\)[/tex] and [tex]\(\cos(A-B) = \frac{4}{5}\)[/tex], we can use trigonometric identities and known values. Here are the step-by-step calculations:

1. Given Values:
[tex]\[ \sin(A+B) = \frac{24}{25} \][/tex]
[tex]\[ \cos(A-B) = \frac{4}{5} \][/tex]

2. Start with [tex]\(\cos(A+B)\)[/tex]:
Since [tex]\(\sin^2(x) + \cos^2(x) = 1\)[/tex], we can find [tex]\(\cos(A+B)\)[/tex]:
[tex]\[ \cos^2(A+B) = 1 - \sin^2(A+B) \][/tex]
[tex]\[ \cos^2(A+B) = 1 - \left(\frac{24}{25}\right)^2 \][/tex]
[tex]\[ \cos^2(A+B) = 1 - \frac{576}{625} \][/tex]
[tex]\[ \cos^2(A+B) = \frac{625 - 576}{625} \][/tex]
[tex]\[ \cos^2(A+B) = \frac{49}{625} \][/tex]
[tex]\[ \cos(A+B) = \sqrt{\frac{49}{625}} = \frac{7}{25} \][/tex]
Since [tex]\(0 < A+B < \frac{\pi}{2}\)[/tex], [tex]\(\cos(A+B)\)[/tex] is positive.

3. Simplify [tex]\(\sin(A-B)\)[/tex]:
Similarly, [tex]\(\sin(A-B)\)[/tex] can be found using:
[tex]\[ \sin^2(A-B) + \cos^2(A-B) = 1 \][/tex]
[tex]\[ \sin^2(A-B) = 1 - \cos^2(A-B) \][/tex]
[tex]\[ \sin^2(A-B) = 1 - \left(\frac{4}{5}\right)^2 \][/tex]
[tex]\[ \sin^2(A-B) = 1 - \frac{16}{25} \][/tex]
[tex]\[ \sin^2(A-B) = \frac{25 - 16}{25} \][/tex]
[tex]\[ \sin^2(A-B) = \frac{9}{25} \][/tex]
[tex]\[ \sin(A-B) = \sqrt{\frac{9}{25}} = \frac{3}{5} \][/tex]
Again, since [tex]\(0 < A-B < \frac{\pi}{2}\)[/tex], [tex]\(\sin(A-B)\)[/tex] is positive.

4. Use Sum-to-Product Formulas:
Recall trigonometric sum-to-product formulas:
[tex]\[ \sin(A+B) = \sin A \cos B + \cos A \sin B \][/tex]
[tex]\[ \cos(A-B) = \cos A \cos B + \sin A \sin B \][/tex]

5. Set Up a System of Equations:
Let [tex]\(x = \sin A\)[/tex] and [tex]\(y = \cos A\)[/tex]:
[tex]\[ \sin A \cos B + \cos A \sin B = \frac{24}{25} \][/tex]
[tex]\[ x \cos B + y \sin B = \frac{24}{25} \][/tex]
[tex]\[ \cos A \cos B + \sin A \sin B = \frac{4}{5} \][/tex]
[tex]\[ y \cos B + x \sin B = \frac{4}{5} \][/tex]

6. Utilize Identities:
Since [tex]\(\cos^2 A + \sin^2 A = 1\)[/tex], let’s find the value to plug back in.
From here, we’re primarily interested in [tex]\(\tan 2A\)[/tex]:
[tex]\[ \tan 2A = \frac{2 \tan A}{1 - \tan^2 A} \][/tex]

7. Find [tex]\(\tan A\)[/tex]:
Using our cosine and sine values derived previously:
[tex]\[ \tan A = \frac{\sin A}{\cos A} = \frac{x}{y} \][/tex]

8. Final Calculation:
The result for [tex]\(\tan 2A\)[/tex]:
[tex]\[ \tan 2A = \frac{2 \tan A}{1 - \tan^2 A} = \frac{48/25}{1 - (24/25)^2} \][/tex]

[tex]\[ \tan^2 2A = \frac{24/25}{1 - (24/25)^2} \][/tex]

[tex]\[ \tan 2A = \frac{48 /25 }{49/25} \][/tex]

The solution we need to find:

[tex]\[ \tan 2A = \frac{48}{7}. \][/tex]

So, the value of [tex]\(\tan 2A\)[/tex] is [tex]\(\boxed{ \text{Note This step still need to add also result for easier representation completion steps from \( \frac{24/25}{3}\)[/tex]}}