$\sin{x}+\cos{y}=1$
và$\cos{x}+\sin{y}=-1.$
Chứng minh rằng $\cos{2x}=\cos{2y}$.Edited by QUANVU, 26-02-2007 - 16:40.
$\sin{x}+\cos{y}=1$
và$\cos{x}+\sin{y}=-1.$
Chứng minh rằng $\cos{2x}=\cos{2y}$.Edited by QUANVU, 26-02-2007 - 16:40.
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