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b. If [tex]\sin 2A = \frac{24}{25}[/tex] and [tex]\sin A = \frac{4}{5}[/tex], then find the value of [tex]\cos A[/tex].

Sagot :

Absolutely, let's go through this step-by-step:

1. Given Information:
- [tex]\(\sin 2A = \frac{24}{25}\)[/tex]
- [tex]\(\sin A = \frac{4}{5}\)[/tex]

2. Double Angle Identity for Sine:
- We know from trigonometric identities that [tex]\(\sin 2A = 2 \sin A \cos A\)[/tex].

3. Setting Up the Equation:
- Substitute the known values into the double angle identity:
[tex]\[ \sin 2A = 2 \sin A \cos A \][/tex]
[tex]\[ \frac{24}{25} = 2 \left(\frac{4}{5}\right) \cos A \][/tex]

4. Solving for [tex]\(\cos A\)[/tex]:
- First, simplify the right-hand side:
[tex]\[ \frac{24}{25} = 2 \cdot \frac{4}{5} \cdot \cos A = \frac{8}{5} \cos A \][/tex]

- Next, isolate [tex]\(\cos A\)[/tex] by dividing both sides of the equation by [tex]\(\frac{8}{5}\)[/tex]:
[tex]\[ \cos A = \frac{\frac{24}{25}}{\frac{8}{5}} \][/tex]

- Simplify the division:
[tex]\[ \cos A = \frac{24}{25} \times \frac{5}{8} = \frac{24 \cdot 5}{25 \cdot 8} = \frac{120}{200} = \frac{3}{5} \][/tex]

5. Final Answer:
- Therefore, the value of [tex]\(\cos A\)[/tex] is:
[tex]\[ \cos A = 0.6 \][/tex]
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