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Introduction to BASIC Curves and Graphs
Coordinate System
Before drawing curves or graphs, the coordinate system should be set.
`SET WINDOW` x1`,` x2`,` y1`,` y2
sets the coordinate system where the range of x coordinate is from x1 to x2, and the range of y coordinate is from y1 to y2.
Coordinate axes
`DRAW axes`
draws the axes of coordinate.
PLOT LINES
PLOT LINES statements draw segments continuously.
A sequential execution of
`PLOT LINES: x,y;`
draws an approximation of a curve.
Example.

    10 DEF f(x)=x^3-x
    20 SET WINDOW -4,4,-4,4
    30 DRAW axes
    40 FOR x=-4 TO 4 STEP 0.01
    50     PLOT LINES: x,f(x);
    60 NEXT x
    70 END

Refer to PLOT LINES