after getting the equation for a plane, solving for z

I have three points that I am using to find the normal and then I have another point that I was using symbolically. After the code below, I need to be able to substitute in values for x and y in order to get z. I need help figuring out how to substitute for symbolic variables or what other function to use in order to be able to substitute but still keep the original expression.

start = [-13627.6  4904.1 1563.141];
middle = [-13630.9  4677.7  1562.681];
finish = [-13550.5  4593  1563.031];
>> normal = cross(start-middle, start-finish);
syms x y z
p = [x y z];
planefunction = dot(normal, p - start)
Z = solve(planefunction,z);

Answer 1

[Paulo Silva]

use the subs function

or do like this

start = [-13627.6  4904.1 1563.141];
middle = [-13630.9  4677.7  1562.681];
finish = [-13550.5  4593  1563.031];
normal = cross(start-middle, start-finish);
syms x y z
p = [x y z];
planefunction = dot(normal, p - start)
Z = solve(planefunction,z);
x=1;y=1; %the values you want for x and y
z=eval(char(Z)) %now with x and y you can get z

[Brittany]

subs works great. thanks!