sina-cosa=√2sin(a-π/4)=√2
a∈(0,π)
a-π/4∈(-π/4,3π/4)
sin(a-π/4)=1
所以 a-π/4=π/2
得 a=3π/4
tana=tan(3π/4)=-1采纳可好？已采纳= =没采纳