1.余弦定理
cosB=(a^2+c^2-b^2)/2ac
ac/(a^2+c^2-b^2)=1/(2cosB)
tanB=sinB/cosB=√3/(2cosB) sinB=√3/2 锐角三角形,所以B=60°
2.
sin（B+10度）[1-根号3*tan（B-10度）]
=sin(70°)[1-√3*tan50°]
=sin(70°)[1-(sin60°/cos60°)*(sin50°/cos50°)]
=sin70°*(1-(sin60°sin50°)/(cos60°cos50°))
=sin70°*(cos60°cos50°-sin60°sin50°)/(cos60°cos50°)
=sin70°*cos110°/(cos60°cos50°)
=-sin70°cos70°/(1/2*cos50°)
=-2sin70°cos70°/cos50°
=-sin140°/cos50°
=-cos50°/cos50°
=-1