若sin (π/4+α)sin(π/4-α)=-1/8,则2sin²α+tanα-1/tanα-1的值为

若sin (π/4+α)sin(π/4-α)=-1/8,则2sin²α+tanα-1/tanα-1的值为
若sin (π/4+α)sin(π/4-α)=-1/8,则2sin²α+tanα-1/tanα-1的值为

若sin (π/4+α)sin(π/4-α)=-1/8,则2sin²α+tanα-1/tanα-1的值为
sin (π/4+α)sin(π/4-α)
=sin (π/4+α)cos (π/4+α)
=1/2sin (π/2+2α)
=-1/2cos2a
后面的式子看不明白是什么