Question

求满足方程(tanx)^4+(tany)^4+2(cotx)^2(coty)^2=3+sin^2 (x+y)的所有实数对

Answer 1

(tanx)^4+(tany)^4>=2(tanx)^2(tany)^2

2(tanx)^2(tany)^2+2/[(tanx)^2(tany)^2]>=4

3+[sin(x+y)]^2