Algebra 2 help!,

$T=\frac12\sqrt{\frac{u}{g}}$

Multiply both sides of the equation by  2 .

$2T=\sqrt{\frac{u}{g}}$

Square both sides of the equation.

$(2T)^2=\frac{u}{g} \\~\\ (2T)(2T)=\frac{u}{g} \\~\\ 4T^2=\frac{u}{g}$

Multiply both sides by  g .

$g\cdot4T^2=u$

Divide both sides by  4T²

$g=\frac{u}{4T^2}$