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The general solution to the quadratic equation
\[
ax^2+bx+c=0
\]
is given by the \textit{quadratic formula}:
\[
x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}
\]
For two sets $A$ and $B$, the \textit{DeMorgan Laws} state that:
\[
(A\cup B)^c=A^c\cap B^c
\]
and
\[
(A\cap B)^c=A^c\cup B^c
\]
Two sets $A$ and $B$ are equal if
\[
A\subseteq B\quad\mbox{and}\quad B\subseteq A
\]
If you don't mind italics you can just use:
\[
A\subseteq B\quad and \quad B\subseteq A
\]
The most important trigonometric identity is:
\[
\sin^2x+\cos^2x=1
\]
Although LaTeX can be very complicated, you can usually ignore what you don't need.
\par
If you don't remember how to specify a symbol, Google 'LaTeX math symbols'
\par 
You can switch to math mode inline by surrounding text with dollar signs: $\sqrt{4-x}$.
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