documentclass[]{report}

usepackage{amsmath}

begin{document}

begin{align}
dot{V} &=, frac{1}{gamma_{2,1}}sigma_{2,1} dot{sigma}_{2,1} + frac{1}{gamma_{2,2}}sigma_{2,2} dot{sigma}_{2,2} + frac{1}{gamma_{2,3}}sigma_{2,3} dot{sigma}_{2,3} notag \
 &= -sigma_{2,1}left [ sigma_{2,1}sin^2(x_1)+sigma_{2,2}sin(x_1)x_2 + sigma_{2,3}sin(x_1)uright ] notag \
 & -sigma_{2,2}left [ sigma_{2,1}sin(x_1)x_2+sigma_{2,2}x_2^2 + sigma_{2,3}x_2 uright ] - sigma_{2,3}left [ sigma_{2,1}sin(x_1)u+sigma_{2,2}x_2u + sigma_{2,3} u^2right ]notag \
end{align}

end{document}