cosx=-4/5x∈(π,3π/2)sinx=-√[1-(-4/5)^2]=-3/5所以[1+tan(x/2)]/[1-tan(x/2)]=[cos(x/2)+sin(x/2)]/[cos(x/2)-sin(x/2)](分子分母同时乘以cos(x/2))=[cos(x/2)+sin(x/2)]^2/[cos(x/2)-sin(x/2)][cos(x/2)+sin(x/...