数学高考第八题怎么做

=(sin^2 b/2+2 sinb/2 cosb/2 +cos^2 b/2)/(cos^2 b/2 -sin^2 b/2)

=(cosb/2 +sinb/2)^2/(cos^2 b/2 -sin^2 b/2)

=(cosb/2+sinb/2)/(cosb/2-sinb/2)

= cosb/2(1+tanb/2)/cosb/2(1-tanb/2)

=(1+tanb/2)/(1-tanb/2)

=(tan 45+tanb/2)/(1-tan 45 tanb/2)

=tan(45+b/2)

∴a=45+b/2

2a-b=90

选b。