giai pt
tan^7 x+cot^7 x=tanx +cotx
=> [TEX]tan^{7}x+\frac{1}{tan^{7}x}-tanx-\frac{1}{tanx}=0[/TEX]
=> [TEX]tanx(tan^{6}-1)+\frac{1}{tanx}(\frac{1}{tan^{6}x}-1)=0[/TEX]
=> [TEX]tanx(tan^{6}-1)-\frac{1}{tanx}.\frac{tan^{6}x-1}{tan^{6}}=0[/TEX]
=> [TEX](tan^{6}x-1)(tanx-\frac{1}{tan^{7}x})=0[/TEX]
=> [TEX](tan^{6}x-1).\frac{tan^{8}x-1}{tan^{7}x}=0[/TEX]
=> ...........................