Điều kiện tự làm$ tanx(tanx - tan3x) = 2 $$\Leftrightarrow sinx(sinx.cos3x - sin3x.cosx) = 2cos^2x.cos3x $$\Leftrightarrow sinx.sin(-2x) = 2cos^2x.cos3x $$\Leftrightarrow -2sin^2x.cosx = 2cos^2x cos3x $$\Leftrightarrow 2sin^2x = 2cosx.cos3x$$\Leftrightarrow 1 - cos2x = cos4x + cos2x$$\Leftrightarrow 2\cos^2 2x + 2\cos 2x -1=0$ nghiệm xấu hoắc
Điều kiện tự làm$ tanx(tanx - tan3x) = 2 $$\Leftrightarrow sinx(sinx.cos3x - sin3x.cosx) = 2cos^2x.cos3x $$\Leftrightarrow sinx.sin(-2x) = 2cos^2x.cos3x $$\Leftrightarrow -2sin^2x.cosx = 2cos^2x cos3x $$\Leftrightarrow sin^2x = cosx.cos3x$$\Leftrightarrow -\dfrac{1}{2}(1 - cos2x) = \dfrac{1}{2}(cos4x + cos2x) $$\Leftrightarrow cos4x = -1 $ coi như xong
Điều kiện tự làm$ tanx(tanx - tan3x) = 2 $$\Leftrightarrow sinx(sinx.cos3x - sin3x.cosx) = 2cos^2x.cos3x $$\Leftrightarrow sinx.sin(-2x) = 2cos^2x.cos3x $$\Leftrightarrow -2sin^2x.cosx = 2cos^2x cos3x $$\Leftrightarrow
2sin^2x =
2cosx.cos3x$$\Leftrightarrow 1 - cos2x = cos4x + cos2x$$\Leftrightarrow
2\cos
^2 2x
+ 2\cos 2x -1
=0$ n
gh
iệm x
ấu ho
ắc