Question

[Le van a]

Đơn giản biểu thức sau:

\(H=cot\left(\alpha-2\pi\right).cos\left(\alpha-\dfrac{3\pi}{2}\right)+cos\left(\alpha-6\pi\right)-2sin\left(\alpha-\pi\right)\)

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Answer 1

[Nguyễn Thị Lan Anh]

H = \(\cot\left(\alpha-2\pi\right)\) . \(\cos\left(\alpha-\dfrac{3\pi}{2}\right)\) + \(\cos\left(\alpha-6\pi\right)\) - 2\(\sin\left(\alpha-\pi\right)\)

⇔H = \(\cot\alpha\). \(\cos\left(\alpha+\dfrac{\pi}{2}-2\pi\right)\) + \(\cos\alpha\) + 2\(\sin\left(\pi-\alpha\right)\)

⇔H = \(\cot\alpha\). \(\cos\left(\alpha+\dfrac{\pi}{2}\right)\) + \(\cos\alpha\) + 2\(\sin\alpha\)

⇔H = \(\cot\alpha\) . (-\(\sin\alpha\)) + \(\cos\alpha\) + 2\(\sin\alpha\)

⇔H = -\(\cos\alpha\) + \(\cos\alpha\) + 2\(\sin\alpha\)

⇔H = 2\(\sin\alpha\)

Vậy H = 2\(\sin\alpha\)