Question

已知tan(π/4+a)=-1/2,求[sin2a-2(cosa)^2]/1+tan a

Answer 1

tan(π/4+a)=（1+tana）/（1-tana）=-1/2

tana=-3

sina=3根号10/10

[sin2a-2(cosa)^2]/1+tan a

=[sin2a-2+2(sina)^2]/1+tan a

=[2(tanα)]/[1+(tanα）^2]+2*90/100-3

=-6/10+18/10-3

=12/10-3

=-1.8