tanɑ ∕(tanɑ-1)=-1
tanα=1-tanα
2tanα=1
tanα=1/2
(sinα)^2=（tanα)^2/[1+(tanα)^2]=(1/4)/(1+1/4)=1/5
(sinɑ)^2+sinɑcosɑ+2
=(sinα)^2+sinα*sinα/tanα+2
=(sinα)^2+(sinα)^2/(1/2)+2
=3(sinα)^2+2
=3*1/5+2
=13/5=2.6