Missing } Inserted?

Question

I wrote

    \begin{align}
    $\lim_{x \to 2} f(x)$ &= $\lim_{x \to 2}\dfrac{2x^2-5x+2}{5x^2-7x-6}$\\
                          &= $\lim_{x \to 2}\dfrac{(x-2)(2x-1)}{(x-2)(5x+3)}$\\
    \end{align}

But apparently I have a missing } and I cannot find it. Help?

Answer 1

When you start a display environment, be it

\begin{equation}

\begin{equation*}

\begin{align}

\begin{align*}

\begin{gather}

\begin{gather*}

and the other display environments, you are already in math mode, so a $ character is illegal.

Type $<formula>$ only for inline math formulas.

So

\begin{align}
\lim_{x \to 2} f(x) &= \lim_{x \to 2}\dfrac{2x^2-5x+2}{5x^2-7x-6} \\
                    &= \lim_{x \to 2}\dfrac{(x-2)(2x-1)}{(x-2)(5x+3)}
\end{align}

Don't add \\ to the last row of a display environment. It's optional in array, but at the outer level in a display environment it would produce an unwanted blank line.