Finding x and y intercepts of each equation: the equation is x+y=3

X intercept is where the line crosses the x axis or where y=0
y intercept is where the line crosses the y axis or where x=0

x+y=3
x intercept
set y to 0
x+0=3
x=3
the x intercept is at x=3

y intercept
set x to 0
0+y=3
y=3
the x intercept is at y=3

Iwould say they are complementary because that’s the division of a 90 degree angle and it’s split between the middle of them