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Calculate the limit:

[tex]\[ \lim_{x \rightarrow \frac{\pi}{2}} \frac{8 \sqrt{2} - (\cos x + \sin x)^7}{\sqrt{2} - \sqrt{2} \sin 2x} \][/tex]


Sagot :

To find the limit of [tex]\(\lim_{x \to \frac{\pi}{2}} \frac{8 \sqrt{2} - (\cos x + \sin x)^7}{\sqrt{2} - \sqrt{2} \sin 2x}\)[/tex], we can follow these steps:

1. Evaluate the behavior of the numerator as [tex]\( x \)[/tex] approaches [tex]\( \frac{\pi}{2} \)[/tex]:

When [tex]\( x \)[/tex] approaches [tex]\( \frac{\pi}{2} \)[/tex]:
- [tex]\(\cos\left(\frac{\pi}{2}\right) = 0\)[/tex]
- [tex]\(\sin\left(\frac{\pi}{2}\right) = 1\)[/tex]

Therefore,
[tex]\[ \cos x + \sin x \rightarrow 0 + 1 = 1 \][/tex]
and consequently,
[tex]\[ (\cos x + \sin x)^7 \rightarrow 1^7 = 1. \][/tex]

Plugging this into the numerator:
[tex]\[ 8\sqrt{2} - (\cos x + \sin x)^7 \rightarrow 8\sqrt{2} - 1. \][/tex]

2. Evaluate the behavior of the denominator as [tex]\( x \)[/tex] approaches [tex]\( \frac{\pi}{2} \)[/tex]:

For the denominator, we note that:
- [tex]\( \sin(2x) = \sin\left(2 \cdot \frac{\pi}{2}\right) = \sin(\pi) = 0 \)[/tex].

Plugging this into the denominator:
[tex]\[ \sqrt{2} - \sqrt{2} \sin(2x) \rightarrow \sqrt{2} - \sqrt{2} \cdot 0 = \sqrt{2}. \][/tex]

3. Combine and simplify:

Our expression now simplifies to:
[tex]\[ \frac{8 \sqrt{2} - 1}{\sqrt{2}}. \][/tex]

Let's perform the division:
[tex]\[ \frac{8 \sqrt{2} - 1}{\sqrt{2}} = \frac{8 \sqrt{2}}{\sqrt{2}} - \frac{1}{\sqrt{2}} = 8 - \frac{1}{\sqrt{2}}. \][/tex]

4. Further simplification:

We can simplify [tex]\(\frac{1}{\sqrt{2}}\)[/tex] by rationalizing the denominator:
[tex]\[ \frac{1}{\sqrt{2}} = \frac{1 \cdot \sqrt{2}}{\sqrt{2} \cdot \sqrt{2}} = \frac{\sqrt{2}}{2}. \][/tex]

Thus, the expression becomes:
[tex]\[ 8 - \frac{\sqrt{2}}{2} = 8 - 0.707 \approx 7.292. \][/tex]

5. Conclusion:

Therefore, the limit is:
[tex]\[ \boxed{7.292893218813452}. \][/tex]
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