设t=tanx,t∈R
则y=1/(t^2-2t+2)
y=1/[(t-1)^2+1]
∵(t-1)^2+1≥1
∴1/[(t-1)^2+1]∈(0,1]
即y=1(tan^2x-2tanx+2) 的值域为(0,1]
对称轴为t=1,且a>0
∴当t≥1,即tanx≥1时y=1(tan^2x-2tanx+2)单调减,
此时x∈(π/4+kπ,π/2+kπ),k∈Z
同理可得当x∈(-π/2+kπ,π/4+kπ),k∈Z时,y=1(tan^2x-2tanx+2) 单调增
设t=tanx,t∈R
则y=1/(t^2-2t+2)
y=1/[(t-1)^2+1]
∵(t-1)^2+1≥1
∴1/[(t-1)^2+1]∈(0,1]
即y=1(tan^2x-2tanx+2) 的值域为(0,1]
对称轴为t=1,且a>0
∴当t≥1,即tanx≥1时y=1(tan^2x-2tanx+2)单调减,
此时x∈(π/4+kπ,π/2+kπ),k∈Z
同理可得当x∈(-π/2+kπ,π/4+kπ),k∈Z时,y=1(tan^2x-2tanx+2) 单调增