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I have this following function:

$$y\ =\ \sqrt{\left|x\right|^{2}}-\cos\left(3x\right)$$

which represents this:

enter image description here

And I need to find the intersection between an straight line created from two coordinates ($ab$ and $cd$) and this formula, something like this:

enter image description here

I only need the first intersection point coordinates ($ef$) (the closest).

On the internet I only find how to intersect circles with other straight lines. How do I do with a function?

I only have $ab$ and $cd$ coords and need to find $ef$.

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    $\begingroup$ In general if you have 2 functions $f(x), g(x)$, the points of intersection between them occur at the zeros of $f(x)-g(x)$. $\endgroup$
    – 79037662
    Sep 27, 2019 at 17:40
  • $\begingroup$ @79037662 how can I represent $ab, cd$ into $g(x)$ ? $\endgroup$
    – CypherPotato
    Sep 27, 2019 at 17:43
  • $\begingroup$ it's a straight line so you can calculate the equation of a line from two points: mathsisfun.com/algebra/line-equation-point-slope.html $\endgroup$
    – graeme
    Sep 27, 2019 at 17:46
  • $\begingroup$ You're asking how to find the equation of a line given two points on it, this website can explain much better than I can: mathsisfun.com/algebra/line-equation-2points.html $\endgroup$
    – 79037662
    Sep 27, 2019 at 17:47
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    $\begingroup$ You should set equal the equations of the curves (the straight line and the function) which obtains no analytical result in general and should be solved numerically. $\endgroup$
    – Mostafa Ayaz
    Sep 27, 2019 at 18:01

1 Answer 1

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You may use point-slope form of line to find the equation of the line. $${{y-y_1}\over x-x_1} = m$$ $${{y-b}\over x-a} = {{b-d}\over {a-c}}$$ Your equation is $y=|x|-cos(3x)$

Substitute y in the equation of the line and solve for x. This will give you the value of e. With e, you can easily find the value of f.

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  • $\begingroup$ Substitute $y$ with what? $\endgroup$
    – CypherPotato
    Sep 27, 2019 at 18:38
  • $\begingroup$ Substitute y with $|x|-cos(3x)$ in the line equation. $\endgroup$
    – Sam
    Sep 27, 2019 at 18:40

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