a.sin(x+2) = 1/3
b.sin3x=1
c.sin(2x/3 – pi/3) =0
d. sin(2x+20*)= -căn 3/2
a.sin(x+2) = 1/3 b.sin3x=1 c.sin(2x/3 – pi/3) =0 d. sin(2x+20*)= -căn 3/2
By Autumn
By Autumn
a.sin(x+2) = 1/3
b.sin3x=1
c.sin(2x/3 – pi/3) =0
d. sin(2x+20*)= -căn 3/2
Đáp án:
a) $\sin (x+2)=\dfrac13$
$\Leftrightarrow\left[\begin{array}{I} x+2=\arcsin\dfrac13+k2\pi\\x+2=\pi-\arcsin\dfrac13+k2\pi\end{array}\right.$
$\Leftrightarrow\left[\begin{array}{I} x=\arcsin\dfrac13-2+k2\pi\\x=\pi-\arcsin\dfrac13-2+k2\pi\end{array}\right.(k\in\mathbb Z)$
Vậy phương trình có nghiệm:
$\left\{\begin{array}{I} x=\arcsin\dfrac13-2+k2\pi\\x=\pi-\arcsin\dfrac13-2+k2\pi\end{array}\right.(k\in\mathbb Z)$
b) $\sin 3x=1$
$\Leftrightarrow 3x=\dfrac{\pi}2+k2\pi$
$\Leftrightarrow x=\dfrac{\pi}6+k\dfrac{2\pi}3$ $(k\in\mathbb Z)$
Vậy phương trình có nghiệm:
$x=\dfrac{\pi}6+k\dfrac{2\pi}3$ $(k\in\mathbb Z)$
c) $\sin\left({\dfrac{2x}3-\dfrac{\pi}3}\right)=0$
$\Leftrightarrow \dfrac{2x}3-\dfrac{\pi}3=k\pi$
$\Leftrightarrow \dfrac{\pi}2+k\dfrac{3\pi}2$ $(k\in\mathbb Z)$
Vậy phương trình có nghiệm:
$\dfrac{\pi}2+k\dfrac{3\pi}2$ $(k\in\mathbb Z)$
d) $\sin(2x+20^o)=-\dfrac{\sqrt3}2$
$\Leftrightarrow\left[\begin{array}{I} 2x+20^o=-60^o+k2\pi\\2x+20^o=180^o-(-60^o)+k2\pi\end{array}\right.$
$\Leftrightarrow\left[\begin{array}{I} x=-40^o+k\pi\\x=110^o+k\pi\end{array}\right. $ $(k\in\mathbb Z)$
Vậy phương trình có nghiệm:
$\left\{\begin{array}{I} x=-40^o+k\pi\\x=110^o+k\pi\end{array}\right. $ $(k\in\mathbb Z)$
Giải thích:
$\sin x=\sin \alpha$
$\Leftrightarrow\left[\begin{array}{I} x=\alpha+k2\pi\\x=\pi-\alpha+k2\pi\end{array}\right.$ $(k\in\mathbb Z)$
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