[tex]\\
$Formula$:
\tan a+\tan b=\frac{\sin(a+b)}{\cos a\cos b}\\
\tan 3x+\tan 5x=\frac{\sin8x}{\cos 3x\cos 5x}\\
2\tan 4x=\frac{\sin8x}{\cos^2 4x}\\
$Ecuatia devine$\\
\frac{\sin8x}{\cos 3x\cos 5x}=\frac{\sin8x}{\cos^2 4x}\\
\\
i)\sin8x=0\Rightarrow \text{etc..}\\
ii)\cos 3x\cos 5x}=\cos^2 4x\\
$Formula$: \cos a\cos b=\frac{1}{2}(\cos(a-b)+\cos(a+b))\\
$Ecuatia devine$:\frac{1}{2}(\cos x+\cos8x)=\frac{1}{2}(1+\cos8x)\\
\Rightarrow \cos8x=1\Rightarrow \text{etc...}
[/tex]
Sper ca te-am ajutat. Trebuie sa mai rezolvi numai ecuatiile acelea fundamentale. Spor!!
