Align a running list of expressions to the left

Question

The following code:

\documentclass[12pt, a4paper, twoside, titlepage]{article}

\usepackage{amsmath}
\begin{document}

  \begin{flalign}
    J(1)=\\
    \sum\limits_{i=1}^{m} (h_\Theta(x^i)-y^i)^2=&&\\
    \sum\limits_{i=1}^{3} (\Theta_1(x^i)-y^i)^2=&&\\
    \frac{1}{3}((1-1)^2+(2-2)^2+(3-3)^2)=&&\\
    \frac{1}{3}(0+0+0)=0
  \end{flalign}

\end{document}

Gives the following equation alignment:

Aligning by the = is great when developing two sides of an equation. However, when developing an expresion line-by-line, I prefer that the expressions will be aligned to the left:

I assume that after seeing my handwriting skills, my need for Latex is self-explanatory.

What have I tried

• Playing with align and flalign
• Reading "Aligning equations with amsmath"
• Reading problem using option fleqn in amsmath package, Use flalign or alignat or align or similar environment to align to the left, Text in flalign/align and How can I use an align environment flush left?

My question

How do I align a running numbered list of expressions, similar to the one listed above, in which the expressions are aligned to the left?

Answer 1

How about this:

\documentclass[12pt, a4paper, twoside, titlepage]{article}

\usepackage{amsmath}
\begin{document}

  \begin{align}
    &J(1)=\\
    &\sum\limits_{i=1}^{m} (h_\Theta(x^i)-y^i)^2=\\
    &\sum\limits_{i=1}^{3} (\Theta_1(x^i)-y^i)^2=\\
    &\frac{1}{3}((1-1)^2+(2-2)^2+(3-3)^2)=\\
    &\frac{1}{3}(0+0+0)=0
  \end{align}

\end{document}