How to judge whether to use the proportional function or the inverse proportional function for the math application problems in the second day of junior high school?
The direct proportional function is Y/X= constant, the general form is Y=aX, the inverse proportional function is xy= constant, and y=a/x, which is a formal difference. Another difference is that the positive proportional function increases when x increases and decreases when y decreases, and the inverse proportional function increases when x decreases and decreases when y decreases. Of course, the images are different. The direct proportional function is a straight line and the inverse proportional function is a curve.