The equation of a line having 'm' as slope and 'c' as y-intercept is y=mx+c.
2x−y+1=0→y=2x+1
So, slope and y-intercept are 2 and 1 respectively.
Sum = 2+1 = 3
x−y+1=0→y=x+1
So, slope and y-intercept are 1 and 1 respectively.
Sum = 1+1 = 2
3x−3y=0→x−y=0→y=x
So, slope and y-intercept are 1 and 0 respectively.
Sum = 1+0 = 1
x−y−1=0→y=x−1
So, slope and y-intercept are 1 and -1 respectively.
Sum = 1-1 = 0