Cost Function

cost function - measures the accuracy of our hypothesis function h_θ(x)

This function is also called the squared error cost function or mean squared error.

We want h_θ(x) - y to be small.

We minimize the cost function J(θ₀θ₁) over θ₀θ₁. J(θ₀θ₁) is a parabolic function. Minimizing it means finding the value of θ₁.