# quadratic curve from matrices determinant

2 views (last 30 days)
laura bagnale on 14 Jun 2021
Commented: laura bagnale on 14 Jun 2021
Hello everyone,
I would like to obtain the quadratic curve coming from the calculation of a 2x2 matrix determinant.
This is what I wrote in my code:
h = @(x,y,z) 3.*(x+5).^2 + (x + 5).*(y - 2) + (y - 2).^2;
syms x y z
w = h(x,y,z)
g = @(x,y,z) (x - 5).^2 - (x - 5).*(y - 3) + (y - 3).^2;
syms x y z
w1 = g(x,y,z)
Dhx = diff(h,x)
Dhy = diff(h,y)
Dgx = diff(h,x)
Dgy = diff(h,y)
p1 = Dhx * Dgy
expand(p1)
p2 = Dhx * Dgy
expand(p2)
exp1 = expand(p1)
exp2 = expand(p2)
Now I should do the difference between exp1 and exp2, but I can't do it.
I am new with the symbolic toolbox, so I have difficulties to pass from symbolic expressions to numerical values.
I guess there is a faster way to calculate the determinant of my matrix and thus get the quadratic function but I don't really know how to find it.
Thank you very much for your support!
Laura
laura bagnale on 14 Jun 2021
Oh OK, thank you very much.
I'm very sorry but I'm new and I didn't understand that it was important!
Thank you again!
Laura

R2021a

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