Question

已知sinx cosx=-1,-兀

Answer 1

sinx * cosx / [(sinx)^2 + (cosx)^2] = -1

1 / (tanx + 1/tanx) = -1 (左边式子上下同除于sinx * cosx)

tanx + 1/tanx = -1

(tanx)^2 + 1 = -tanx

(tanx)^2 + tanx + 1 =0

(tanx + 1/2)^2 + 3/4 =0

tanx 无解.

题目错了吧.