f(X)=2sinxcosx+cos2x
f(α/2)=√2/2
2sinα/2cosα/2+cosα=√2/2
sinα+cosα=√2/2
cosα=√2/2-sinα
1-sin^2α=1/2-√2sinα+sin^2α
sin^2α-√2/2sinα-1/4=0
(sinα-√2/4)^2-3/8=0
sinα=√2/4-√6/4(舍去) ,
sinα=√2/4+√6/4
f(X)=2sinxcosx+cos2x
f(α/2)=√2/2
2sinα/2cosα/2+cosα=√2/2
sinα+cosα=√2/2
cosα=√2/2-sinα
1-sin^2α=1/2-√2sinα+sin^2α
sin^2α-√2/2sinα-1/4=0
(sinα-√2/4)^2-3/8=0
sinα=√2/4-√6/4(舍去) ,
sinα=√2/4+√6/4