Question

tanx = -1

Answer 1

\[\tan x=\frac{\sin x}{\cos x}\]
So if the tangent of x is equal to -1, then sin x/cos x is 1 as well.

Now you'd just try to figure out where sine and cosine are the same number, but just with different signs (positive or negative) which in this case would be sqrt 2/2, - sqrt 2/2 OR - sqrt2 /2, sqrt 2/2.
Long story short, find where sin x/cos x is equal to 1 on here : http://math.ucsd.edu/~wgarner/math4c/theunitcircle.htm