You would use ‘Xliner’ if you need to do the linear regression using the mldivide function, or ‘\’ operator:
sampleData = 100;
x = linspace(-5,5);
y= 1.6 * x .^2 + 2.5*x+6;
dataset = randn(2,sampleData);
Xliner = [x; ones(1,sampleData)]';
p = Xliner\[dataset(1,:)+y]';
Notice the transpose (') operator.
It seems you were given incomplete information. See the documentation for mldivide for the details on how it works and how to use it.