Question

prove α = cosθ + isinθ for 0 < θ < 2π, show that 1+α/1−α = i cot (θ/)2

Answer 1

It means to determine if the value of a trigonometric function is positive or negative; for example, since

sin

(

3

π

2

)

=

−

1

<

0

, its sign is negative, and since

cos

(

−

π

3

)

=

1

2

>

0

, its sign is positive.

I hope that this was helpful.