Question 26730
WE SAY X VARIES DIRECTLY AS Y IF X=K*Y,WHERE K IS A CONSTANT..HERE WE HAVE 
AX-BY=C..OR...AX=BY+C...OR...X=(BY+C)/A = (B/A)Y+(C/A)..BUT FOR DIRECT PROPORTION X=K*Y...HENCE C/A=0...OR...C=0