The line with equation x+y=0 coincides with the terminal side of an angle 0 in standard position in quadrant II.

What is the value of tan0?

tan O = - 1.

Step-by-step explanation:

x + y = 0

y = - x

This is a straight line passing through the origin with a slope of - 1.

So the angle O in quadrant 2 = 135 degrees.

and it's tangent is - 1.