Question

已知tan（π/4+a)=1/2 1:求tana 2：求sin2a-cos^2a/1+cos2a的值

Answer 1

(1)tan（π/4+a)=1/2 1得tana =-1/3
(2)由倍角公式得sin2a-cos^2a/1+cos2a=(2sinacos-cos^2a)/(2cos^a)
=tana-1/2=-1/3-1/2=-5/6.

Answer 2

一∵tan=(π/4+a)=/2
∴①π/4+a=2kπ+π/4
∴a=2kπ
②∵π/4+a=π5/4+2kπ=(2k+1)π+π/4
∴a=(2k+1)π
tana=0
二sin2a-cos2a/1+coa2a
=sin2a-coa2a/coa2a+sin2a+cos2a
=tan2a-1/2tan2a(由上步分子分母都除以cos2a得到)
=-(1/2)