LaTeX Equation left aligned with smaller fonts size

I have the sample below, When I compile and run, each step of the equation is left aligned with smaller fonts. What I'm trying to achieve is, each step of the equation should appear on a line by itself, normal fonts aligned at = sign.

\documentclass{article}
\usepackage[margin=0.5in]{geometry}
\begin{document}
\begin{align*}
\sum_{i=1}^{k+1} i^{3} = \left(\sum_{i=1}^{n} i^{3}\right) +  i^3\\
&=& \frac{k^{2}(k+1)^{2}}{4} + (k+1)^3
&=& \frac{k^{2}(k+1)^{2} + 4(k+1)^3}{4}\\
&=& \frac{(k+1)^{2}(k^{2} + 4k + 4)}{4}\\
&=& \frac{(k+1)^{2}(k+2)^{2}}{4}\\
\end{align*}

This proves that Eq. (3) holds.  By induction, Eq (1) holds for all positive integers $n$
\end{document}

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Welcome to TeX.SE. Instead of equation* use align* and use a single & before the =. Also, please post a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. – Peter Grill Jan 31 at 14:58
This code will produce several error messages and typeset a single line that goes beyond the page boundary, but no “smaller font size”. – egreg Jan 31 at 15:02
@PeterGrill I posted a MWE. After applying align* I still get the error – hello Jan 31 at 15:05
Use a single & and you need the ams math package, – Peter Grill Jan 31 at 15:15

You're using the syntax of eqnarray, and are forgetting to load amsmath; compiling your example produces scores of errors and the output is almost arbitrary.

\documentclass{article}
\usepackage[margin=0.5in]{geometry}
\usepackage{amsmath}

\begin{document}

\begin{align*}
\sum_{i=1}^{k+1} i^{3}
&= \biggl(\sum_{i=1}^{n} i^{3}\biggr) +  i^3\\
&= \frac{k^{2}(k+1)^{2}}{4} + (k+1)^3 \\
&= \frac{k^{2}(k+1)^{2} + 4(k+1)^3}{4}\\
&= \frac{(k+1)^{2}(k^{2} + 4k + 4)}{4}\\
&= \frac{(k+1)^{2}(k+2)^{2}}{4}
\end{align*}

\end{document}


Note that the trailing i^3 in the first row should be (k+1)^3

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Thanks for pointing out the maths. It works. – hello Jan 31 at 15:21