The <em>first coordinate</em> is the X axis coordinate that is <em>right</em> to left. So if you go to the right it is getting <em>more positive. </em>You <em>add</em> if it gets more positive.<em> </em>The <em>second coordinate</em> is the Y axis coordinate and if it goes up it is increasing as well. If it <em>increases</em> you are also <em>adding</em>.
