Share JSXGraph: example "Inequalities (half-planes)"

JSXGraph
Share JSXGraph: example "Inequalities (half-planes)"
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Inequalities (half-planes)

Have also a look at "Inequalities (function graphs)".
To graph a *half-plane* write the separating line in the form `ax + by + c = 0` and construct it with ``` var line = board.create('line', [c, b, a]), ``` Then, ``` ineq = board.create('inequality', [line]); ``` shows the points `(x,y)` with `ax + by + c <= 0`. If one wants to show *greater than*, i.e. plot the points `(x,y)` with `ax + by + c >= 0` , the attribute `inverse:true` can be used: ``` var line = board.create('line', [c, b, a]), ineq = board.create('inequality', [line], {inverse:true}); ``` In the following example, two lines are shown. - The blue line has the equation `y = 2x + 3` or `2x - 1y + 3 = 0`, - the black line has the equation `x = 3` or `1x + 0y - 3 = 0`. For these equations, the inequalities plotted are - `2x - y + 3 <= 0` (less than form hence don't add `inverse: true`) - yellow region and - `1x + 0y - 3 >= 0` (greater than form hence do add "inverse: true") - red region.
// Define the id of your board in BOARDID

const board = JXG.JSXGraph.initBoard(BOARDID, {
    boundingbox: [-5, 5, 5, -5],
    axis: true
});

// Line y = 2x + 3 or 
// 2x - 1y + 3 = 0
var line1 = board.create('line', [3, 2, -1]); 

// Plot the area 2x - y + 3 <= 0
var ineq1 = board.create('inequality', [line1], {fillColor: 'yellow'}); 

// Vertical line x = 3 or 
// 1x + 0y - 3 = 0
var line2 = board.create('line', [-3, 1, 0], {strokeColor: 'black'}); 

// Plot the area 1x + 0y - 3 >= 0
var ineq2 = board.create('inequality', [line2], {inverse: true, fillColor: 'red'});