Question
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\( \sin x - \cos x = 1 \quad | \cdot \frac { \sqrt { 2 } } { 2 } \)

Ask by Fleming Pena. in Russia
Jan 23,2025

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Answer

Решения уравнения \( \sin x - \cos x = 1 \) являются: \[ x = \frac{\pi}{2} + 2\pi n \quad \text{или} \quad x = \pi + 2\pi n, \quad n \in \mathbb{Z} \]

Solution

Решим уравнение: \[ \sin x - \cos x = 1 \] Для упрощения воспользуемся умножением обеих частей уравнения на \(\frac{\sqrt{2}}{2}\): \[ \left( \sin x - \cos x \right) \cdot \frac{\sqrt{2}}{2} = 1 \cdot \frac{\sqrt{2}}{2} \] Левая часть преобразуется с использованием формулы преобразования разности синуса и косинуса: \[ \sin x \cdot \frac{\sqrt{2}}{2} - \cos x \cdot \frac{\sqrt{2}}{2} = \frac{\sqrt{2}}{2} \sin x - \frac{\sqrt{2}}{2} \cos x = \sin\left(x - \frac{\pi}{4}\right) \] Таким образом, уравнение принимает вид: \[ \sin\left(x - \frac{\pi}{4}\right) = \frac{\sqrt{2}}{2} \] Теперь найдём решения этого уравнения. Мы знаем, что \(\sin \theta = \frac{\sqrt{2}}{2}\) имеет решения: \[ \theta = \frac{\pi}{4} + 2\pi n \quad \text{или} \quad \theta = \frac{3\pi}{4} + 2\pi n, \quad n \in \mathbb{Z} \] Подставляя \(\theta = x - \frac{\pi}{4}\), получаем: \[ x - \frac{\pi}{4} = \frac{\pi}{4} + 2\pi n \quad \Rightarrow \quad x = \frac{\pi}{2} + 2\pi n \] \[ x - \frac{\pi}{4} = \frac{3\pi}{4} + 2\pi n \quad \Rightarrow \quad x = \pi + 2\pi n \] Таким образом, общее решение уравнения: \[ x = \frac{\pi}{2} + 2\pi n \quad \text{или} \quad x = \pi + 2\pi n, \quad n \in \mathbb{Z} \]

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Bonus Knowledge

Let's explore the equation \( \sin x - \cos x = 1 \) and see what we can do. First, add \( \cos x \) to both sides to get \( \sin x = \cos x + 1 \). Next, we can square both sides to simplify our trigonometric expression, leading to \( \sin^2 x = (\cos x + 1)^2 \). When you apply the Pythagorean identity \( \sin^2 x + \cos^2 x = 1 \), you get a quadratic in terms of \( \cos x \). Solving it can provide roots that lead to specific angles for \( x \). And remember, a common mistake here is neglecting to check for extraneous solutions after squaring both sides! Sometimes squaring can introduce new solutions that don't actually work in the original equation, so always plug those back into the starting equation to verify. It's like making sure the cake you just baked is actually fluffy and delicious!

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