# Difference between revisions of "Extended mean value theorem"

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+ | The ''extended mean value theorem'' (also called ''Cauchy's mean value theorem'') is: | ||

+ | For continuous functions | ||

+ | :<math> f, g: [a,b] \to \mathbb{R}</math> | ||

+ | that are differentiable on the open interval <mtah>(a,b)</math> | ||

+ | |||

<jsxgraph width="600" height="400" box="box"> | <jsxgraph width="600" height="400" box="box"> | ||

var board = JXG.JSXGraph.initBoard('box', {boundingbox: [-5, 10, 7, -6], axis:true}); | var board = JXG.JSXGraph.initBoard('box', {boundingbox: [-5, 10, 7, -6], axis:true}); |

## Revision as of 18:20, 29 January 2019

The *extended mean value theorem* (also called *Cauchy's mean value theorem*) is:
For continuous functions

- [math] f, g: [a,b] \to \mathbb{R}[/math]

that are differentiable on the open interval <mtah>(a,b)</math>

### The underlying JavaScript code

```
var board = JXG.JSXGraph.initBoard('box', {boundingbox: [-5, 10, 7, -6], axis:true});
var p = [];
p[0] = board.create('point', [0, -2], {size:2});
p[1] = board.create('point', [-1.5, 5], {size:2});
p[2] = board.create('point', [1, 4], {size:2});
p[3] = board.create('point', [3, 3], {size:2});
// Curve
var fg = JXG.Math.Numerics.Neville(p);
var graph = board.create('curve', fg, {strokeWidth:3, strokeOpacity:0.5});
// Secant
line = board.create('line', [p[0], p[3]], {strokeColor:'#ff0000', dash:1});
var df = JXG.Math.Numerics.D(fg[0]);
var dg = JXG.Math.Numerics.D(fg[1]);
// Usually, the extended mean value theorem is formulated as
// df(t) / dg(t) == (p[3].X() - p[0].X()) / (p[3].Y() - p[0].Y())
// We can avoid division by zero with that formulation:
var quot = function(t) {
return df(t) * (p[3].Y() - p[0].Y()) - dg(t) * (p[3].X() - p[0].X());
};
var r = board.create('glider', [
function() { return fg[0](JXG.Math.Numerics.root(quot, (fg[3]() + fg[2]) * 0.5)); },
function() { return fg[1](JXG.Math.Numerics.root(quot, (fg[3]() + fg[2]) * 0.5)); },
graph], {name: '', size: 4, fixed:true, color: 'blue'});
board.create('tangent', [r], {strokeColor:'#ff0000'});
```