You have the following equation:
[tex]3x+4y=0[/tex]To write the previous equation in a function form consists in solving for y, just as follow:
3x + 4y = 0 subtract 3x both sides
4y = -3x divide by 4 both sides
y = -3/4 x
Hence, the function for of the given equation is:
y = -3/4 x
