alignamsmathmath-mode
I want to centre the formula inside the equals. So far I have
\begin{alignat*}{2}
v_2(16)&=\frac{2}{5}[v_3(32)+v_3(8)] &&= 0, \\
v_2(4)&=\frac{2}{5}[v_3(8)+v_3(2)] &&= 1.20,\\
v_2(1)&=\frac{2}{5}[v_3(2)+v_3(0.50)] &&= 3.
\end{alignat*}
Basically I have
A =BBB = CC
A =B = CCCC
but I want
A = BBB = CC
A = B =CCCC
The ampersand & does not only mark alignment positions, it further separates columns. So, with alignat, your example could look like:
\begin{alignat}{2}
A &= B & &= C \\
D &= E & &= F
\end{alignat}
The agument to alignat stands for the number of columns.
You could use ordinary equation and/or equation* environments for the first and last equation. Also, if every single line in an align environment gets a \notag statement to suppress an equation number, it's much better to use an align* environment and drop all those \notag statements.
\documentclass[a4paper,oneside,11pt]{report}
\usepackage[cm]{fullpage}
\usepackage{lmodern,amsmath,amssymb}
\usepackage{a4wide}
\setlength{\marginparwidth}{3cm}
\setlength{\topmargin}{0cm}
\setlength{\voffset}{0cm}
\setlength{\headsep}{0cm}
\begin{document}
\begin{equation*}
F_{x_t}(h-h_3) + (F_{z_t} + mg\cos\phi - 2F_{z_1})a_2 - 2h(F_{x_1} + F_{x_2}) - 2F_{z_1}a_1 - F_{z_t}(a_2 + b_1) = 0
\end{equation*}
\begin{align*}
2F_{z_1}(a_1 + a_2) &= F_{x_t}(h - h_3) + (F_{z_t} + mg\cos\phi)a_2 -2h(F_{x_1} + F_{x_2}) - F_{z_t}(a_2 + b_1) \\
&= A_2\sin\phi(h - h_3) + mga_2\cos\phi - 2hA_1\sin\phi - b_1(A_3\sin\phi + B_3\cos\phi) \\
&= \sin\phi\big(A_2(h - h_3) -2hA_1 -b_1A_3 \big) + \cos\phi \big(mga_2 - b_1B_3 \big)
\end{align*}
\begin{equation}
\therefore F_{z_1} = A_4\sin\phi + B_4\cos\phi
\end{equation}
\end{document}
Addendum If you want to eliminate the extra whitespace between the groups of equations, you could proceed by using a split environment inside a gather environment (with \notag directives for all but the final expression):
\documentclass[a4paper,oneside,11pt]{report}
\usepackage[cm]{fullpage}
\usepackage{lmodern,amsmath,amssymb}
\usepackage{a4wide}
\setlength{\marginparwidth}{3cm}
\setlength{\topmargin}{0cm}
\setlength{\voffset}{0cm}
\setlength{\headsep}{0cm}
\begin{document}
\begin{gather}
F_{x_t}(h-h_3) + (F_{z_t} + mg\cos\phi - 2F_{z_1})a_2 - 2h(F_{x_1} + F_{x_2}) - 2F_{z_1}a_1 - F_{z_t}(a_2 + b_1) = 0\notag\\
\begin{split}
2F_{z_1}(a_1 + a_2) &= F_{x_t}(h - h_3) + (F_{z_t} + mg\cos\phi)a_2 -2h(F_{x_1} + F_{x_2}) - F_{z_t}(a_2 + b_1) \notag\\
&= A_2\sin\phi(h - h_3) + mga_2\cos\phi - 2hA_1\sin\phi - b_1(A_3\sin\phi + B_3\cos\phi) \notag\\
&= \sin\phi\big(A_2(h - h_3) -2hA_1 -b_1A_3 \big) + \cos\phi \big(mga_2 - b_1B_3 \big) \end{split} \notag\\
\therefore F_{z_1} = A_4\sin\phi + B_4\cos\phi
\end{gather}
\end{document}
Best Answer
To have each of the three "columns" centered, you could use the
arrayenvironment. Note (i) the specification of the=column dividers in the header of the array environment, to ensure math-appropriate spacing, and (ii) the reset of the\arraystretchparameter to get a look that's appropriate for a group of displayed equations.If you want to typeset the left-most column flush-right against the first
=sign and the right-most column flush-left against the second=sign, you could set{r @{{}={}} c @{{}={}} l}as the array header specification.Rather than center-set the middle portions of the equations, I would actually recommend maintaining the
alignat*environment while adding a further alignment point, at the+sign. I'd also use\tfracrather thanfrac: