KeCheck.m

x1 = 0;   y1 = 0;
x2 = 100;   y2 = 75; 
x3 = 0;   y3 = 100; 

k=0.05
t = 10 

detJ = x1*(y2-y3)+x2*(y3-y1)+x3*(y1-y2); 
detJ

Ke1 = zeros(3); 

Ke1(1,1) = (x3-x2)^2+ (y2-y3)^2; 
Ke1(1,2) = (x3-x2)*(x1-x3)+(y2-y3)*(y3-y1);
Ke1(1,3) = (x3-x2)*(x2-x1)+(y2-y3)*(y1-y2);
Ke1(2,1) = (x3-x2)*(x1-x3)+(y2-y3)*(y3-y1);
Ke1(2,2) = (x1-x3)^2 + (y3-y1)^2; 
Ke1(2,3) = (x1-x3)*(x2-x1)+(y3-y1)*(y1-y2);
Ke1(3,1) = (x3-x2)*(x2-x1)+(y2-y3)*(y1-y2);
Ke1(3,2) = (x1-x3)*(x2-x1)+(y3-y1)*(y1-y2);
Ke1(3,3) = (x2-x1)^2 + (y1-y2)^2; 


Kecheck = (k*t/(2*detJ))*Ke1;

Kecheck