To have infinitely many solutions the two equations have to describe the same line, the same slope and the same y-intercept...So any multiple of the original equation will give two lies that have infinitely many solutions, because they are in fact the same line...
3x+9y=-8
9y=-3x-8
y=(-3x-8)/9 now you can multiply both the numerator and denominator by any real value of x and produce a line that is the same as this line. For example:
y=-5*(-3x-8)/(-5*9)
y=(15x+40)/(-45) but any of the infinite possible multiples will do...
