

Cho tam giác nhọn ABC, chứng minh:
[tex]\frac{tan(A)^{2}+tan(B)^{2}}{tan(A)^{4}+tan(B)^{4}}+\frac{tan(B)^{2}+tan(C)^{2}}{tan(B)^{4}+tan(C)^{4}}+\frac{tan(A)^{2}+tan(C)^{2}}{tan(A)^{4}+tan(C)^{4}}\leq 1[/tex]
[tex]\frac{tan(A)^{2}+tan(B)^{2}}{tan(A)^{4}+tan(B)^{4}}+\frac{tan(B)^{2}+tan(C)^{2}}{tan(B)^{4}+tan(C)^{4}}+\frac{tan(A)^{2}+tan(C)^{2}}{tan(A)^{4}+tan(C)^{4}}\leq 1[/tex]