when i try to plot the line of each equation while changing the value of thea i am not able to do it, but i able to plot the scattered point graphs, Why so?

Could you please describe the problem a little more?

Sir, Actually I am trying to find the value of theta which fits best for the equation using batch gradient descent method, So i wanted to see how the value of theta converges and tried to plot the line. But I am unable to do so, why?