[3/（sin140°）^2-1/(cos140°）^2]*1/sin10°=[3(cos40°）^2-(sin40°）^2]/(sin40°cos40°）^2*1/sin10°=4（1+2cos80°）/[(sin80°）^2*sin10°]=4(1+2sin10°）/[(cos10°）^2*sin10°]=8(1+2sin10°）/(sin...