[tex]sin(x-\frac{\pi}{8})cos(x-\frac{\pi}{8})=\frac{sin(2x-\frac{\pi}{4})}{2}[/tex]
[tex]2sin^2(x-\frac{\pi}{8})=1-cos(2x-\frac{\pi}{4})[/tex]
thay zo => ez r
[tex]sin(x-\frac{\pi}{8})cos(x-\frac{\pi}{8})=\frac{sin(2x-\frac{\pi}{4})}{2}[/tex]
[tex]2sin^2(x-\frac{\pi}{8})=1-cos(2x-\frac{\pi}{4})[/tex]
thay zo => ez r