Answer:
y = -x
Explanation:
y = mx + b is slope-intercept form. So we need to get the x from the left to the right side of the equation. You were given the equation:
x + y = 0
SUBTRACT x from both sides of the equation.
y = -x
which is your answer. If you must then find the slope, it is beside the x, so it is -1 and the b is the y-intercept. In this case it is zero. So the line this equation represents would cross the y-axis at 0.