Answer
$x + y = 1$
Work Step by Step
The slope is the vertical movement divided by the horizontal movement, from the coordinates of the intersections we can draw the conclusion that the vertical movement is $0 - a = -a$ and the horizontal movement is $a - 0 = a$ so the slope is $-a \div a = -1$. This means the equation for the required graph is $y = -x + a$, if we enter the coordinates (-3, 4) this gives us
$4 = 3 + a$
$a = 1$
When you enter this in the equation from exercise 48 you get $x + y = 1$
