Question 156360
x + y < 1

becomes y < 1 - x when you subtract x from both sides of the equation.

to find the demarc line change the equation to y = 1 - x and plot the graph.

some graph plots .................

x         y

-10     +11
-5      +6
-1      +2
 0      +1
+1       0
+5      -4
+10     -9
+12     -11

y is a line with a negative slope.
as x gets larger y gets smaller.

to solve the equation now look for y < 1 - x

for y to be smaller it has to be below the line so you would shade the area below the line that is created to get the answer.

for example, when x is +10 y would be less than -9 to satisfy the equation of y < 1 - x.

going back to the original equation of x + y < 1.

let x be 10 and y be -10 (smaller than -9).

then 10 + (-10) = 10 - 10 = 0 which is < 1.