1 reply to this topic

[lilolilo]

$(\frac{sin2x+cos4x}{sin3x+cos3x})^{2}= 2\sqrt{2}sin(x+\frac{\pi }{4})+3$

Edited by lilolilo, 09-04-2014 - 20:58.

[Kaito Kuroba]

$(\frac{sin2x+cos4x}{sin3x+cos3x})^{2}= 2\sqrt{2}sin(x+\frac{\pi }{4})+3$

pttd:

$\left (\frac{\sin 2x+\cos 4x}{\sin 3x+\cos 3x} \right )^2=2( \sin x+ \cos x)+3 \Leftrightarrow (\cos x-\sin x)^2=2(\sin x+\cos x)+3 \Leftrightarrow 1-2\sin x.\cos x=2(\sin x+\cos x)+3$

sau đó đặt $\sin x+\cos x =t$

đến đây là OK rồi!!!!