# How to draw a vertical line from the intersection of two curves in a graph, when manipulate is used [closed]

I have a manipulate function that creates two lines in a x-y coordinates system, what I want know is a vertical line pointing to the x-axis-intercept, where those two lines intercept

## closed as off-topic by corey979, Henrik Schumacher, José Antonio Díaz Navas, m_goldberg, Kuba♦Apr 10 '18 at 19:48

This question appears to be off-topic. The users who voted to close gave this specific reason:

• "This question cannot be answered without additional information. Questions on problems in code must describe the specific problem and include valid code to reproduce it. Any data used for programming examples should be embedded in the question or code to generate the (fake) data must be included." – corey979, Henrik Schumacher, José Antonio Díaz Navas, Kuba
If this question can be reworded to fit the rules in the help center, please edit the question.

• I'm sure you can get quite far searching around for "lines intersection" and "vertical line". Have you tried anything? Additionally, how do you expect to get help if we don't know how your lines are represented? Please do the searching and let us know where exactly are you stuck. – Kuba Apr 10 '18 at 10:32

f = Sin;
g = Cos;
Manipulate[Normal[Plot[{a f[x],b g[x]}, {x, -2 Pi, 2 Pi},
MeshFunctions -> {a f[#] -b g[#] &}, Mesh -> {{0}},
MeshStyle -> PointSize[Large]]] /. Point[x_] :>
{Thickness[.01], Red, CapForm["Round"], Line[{{x[[1]], 0}, x}], Black, Point[x]},
{{a, 1}, -2, 2}, {{b, 1}, -2, 2}]


Variation on @kglr's approach (somewhat simpler, but you also get additional boundary edges):

f = Sin;
g = Cos;
Manipulate[
ParametricPlot[{{x, a f[x] t}, {x, b g[x] t}},
{x, -2 Pi, 2 Pi}, {t, 0, 1},
MeshFunctions -> {a f[#] - b g[#] &}, Mesh -> {{0}},