The #x and y# chart is probably one of your best friend when it comes to graphing functions. When you graph simple functions such at #y= -2x# you don't necessarily need the x and y chart. Simply applying the concept of rise/run=slope is good enough.
As for the #x and y# chart.
graph{y= -2x [-10, 10, -4.99, 5.01]}
Using your function #y=-2x#, substitute the x value or the x coordinate into the function (replace #x# with the desired coordinate).
The answer #y=?# is basically your #y# coordinate that corresponds with the x coordinate you plugged in.
for ex. #x= 5 # #-> # #y=-2*5 # #-># # y= -10 # coordinate: #(5,-10)#
And by performing simple multiplications, you would find the #x and y #coordinates. Then simply locate the coordinate on the coordinate plane.
Important: x value is based on your decision. Usually the x values are given to you to find the corresponding y coordinate.
I'm not too great at explaining math, hope it helped.
