How to find the zero vaue of a plot?

I have 2 vetors X ,Y plotted Y vs X.

The plot it's made by 2 differrent straight line.

I would like to find the "zero- value"

X=[0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20];
Y=[-0.88 -0.7489 -0.6178 -0.4867 -0.3556 -0.2245 -0.0934 0.0378 0.1689 0.3 0.4311 0.5182 0.6053 0.6924 0.7795 0.8666 0.9537 1.0408 1.1279 1.2150 1.3022];
plot(A,B

Aussuming that Y=f(X) i would like to find Xo for having Y(Xo)=0

I have not the function equation, and i know it would be easy to directly find it in this case, but i am looking for a way to find the 'zero' value of the x-axis for any 2 set of numbers X, Y

Answer 1

[Les Beckham]

X=[0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20];
Y=[-0.88 -0.7489 -0.6178 -0.4867 -0.3556 -0.2245 -0.0934 0.0378 0.1689 0.3 0.4311 0.5182 0.6053 0.6924 0.7795 0.8666 0.9537 1.0408 1.1279 1.2150 1.3022];
plot(X, Y)
% Find the value of x corresponding to Y = 0
x0 = interp1(Y, X, 0)

x0 = 6.7119

hold on
plot(x0, 0, 'r*')
grid on