( TXĐ là tập xác định nhá mn ) 1, TXĐ của hàm số y = 3 / sin bình x – cos bình x 2, TXĐ của hàm số y = tanx / cosx – 1 3, TXĐ của hàm số y = cotx / co

1.

ĐK: $\sin^2x-\cos^2x\ne 0$

$\Leftrightarrow \dfrac{1-\cos2x-1-\cos2x}{2}\ne 0$

$\Leftrightarrow \cos2x\ne 0$

$\Leftrightarrow x\ne\dfrac{\pi}{4}+\dfrac{k\pi}{2}$

$\to D=\mathbb{R}$ \ $\{\dfrac{\pi}{4}+\dfrac{k\pi}{2}\}$

2.

ĐK: $\cos x\ne 0;\cos x\ne 1$

$\Leftrightarrow x\ne\dfrac{\pi}{2}+k\pi; x\ne k2\pi$

$\to D=\mathbb{R}$ \ $\{\dfrac{\pi}{2}+k\pi; k2\pi\}$

3.

ĐK: $\sin x\ne 0;\cos x\ne 0$

$\Leftrightarrow \sin2x\ne 0$

$\Leftrightarrow x\ne \dfrac{k\pi}{2}$

$\to D=\mathbb{R}$ \ $\{\dfrac{k\pi}{2}\}$

4.

ĐK: $\sin x-\cos x\ne 0$

$\Leftrightarrow \sqrt2\sin(x-\dfrac{\pi}{4})\ne 0$

$\Leftrightarrow x\ne \dfrac{\pi}{4}+k\pi$

$\to D=\mathbb{R}$\ $\{\dfrac{\pi}{4}+k\pi\}$ 

5.

ĐK: $x\ge 0$

$\to D=[0;+\infty)$

6.

ĐK: $\cos x\ne 0$

$\Leftrightarrow x\ne \dfrac{\pi}{2}+k\pi$

$\to D=\mathbb{R}$ \ $\{\dfrac{\pi}{2}+k\pi\}$ 

7.

ĐK: $\cos x\ne 1$

$\Leftrightarrow x\ne k2\pi$

$\to D=\mathbb{R}$ \ $\{k2\pi\}$ 

8.

ĐK: $\cos(2x-\dfrac{\pi}{3})\ne 0$

$\Leftrightarrow x\ne \dfrac{5\pi}{12}+\dfrac{k\pi}{2}$

$\to D=\mathbb{R}$ \ $\{\dfrac{5\pi}{12}+\dfrac{k\pi}{2}\}$ 

9. 

ĐK: $\cos 2x\ne 0$

$\Leftrightarrow x\ne \dfrac{\pi}{4}+\dfrac{k\pi}{2}$

$\to D=\mathbb{R}$ \ $\{\dfrac{\pi}{4}+\dfrac{k\pi}{2}\}$ 

10. 

ĐK: $\sin x\ne -1$

$\Leftrightarrow x\ne \dfrac{3\pi}{2}+k2\pi$

$\to D=\mathbb{R}$ \ $\{\dfrac{3\pi}{2}+k2\pi\}$ 

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