Cho sin x = 1/căn5 và sin y = 1/căn10. Tính x+y

$\sin x=\dfrac{1}{\sqrt5}$

$\Rightarrow \cos x=\sqrt{1-\sin^2x}=\dfrac{2}{\sqrt5}$

$\sin y=\dfrac{1}{\sqrt{10}}$

$\Rightarrow \cos y=\dfrac{1-\sin^2y}=\dfrac{3}{\sqrt{10}}$

$\Rightarrow \sin(x+y)=\sin x.\cos y +\cos x.\sin y=\dfrac{\sqrt2}{2}$

$\Rightarrow x+y=\dfrac{\pi}{4}+k2\pi$ hoặc $x+y=\dfrac{3\pi}{4}+k2\pi$